Revert mocha to v7.0.1

In mocha >= 7.1.0, exceptions thrown in test hooks (eg. a `beforeEach`
hook) cause the tests to hang without printing any useful exception
details.

From my notes in a Slack investion:

> The karma-mocha package is responsible for running mocha by calling
> mocha.setup() before the test modules are evaluated and then mocha.run()
> after they are evaluated to actually run the tests, as well as listening
> for test events from Mocha’s “runner” and reporting them back to Karma.
> When the beforeEach hook fails, the runner emits a “fail” event which
> karma-mocha receives. karma-mocha then attempts to emit a “test end”
> event and that ends up triggering an exception in a call to
> test.retriedTest() in code which was added in
> https://github.com/mochajs/mocha/pull/4181/files.

Until this issue is resolved, pin mocha to a version that doesn't
trigger this problem.

package.json

@@ -75,7 +75,7 @@
     "katex": "^0.11.0",
     "lodash.debounce": "^4.0.3",
     "loose-envify": "^1.4.0",
-    "mocha": "^7.0.0",
+    "mocha": "7.0.1",
     "npm-packlist": "^2.0.1",
     "postcss": "^7.0.13",
     "postcss-url": "^8.0.0",

yarn.lock

@@ -5079,14 +5079,7 @@ lodash@^4.15.0, lodash@^4.17.13, lodash@^4.17.14, lodash@^4.17.15:
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.15.tgz#b447f6670a0455bbfeedd11392eff330ea097548"
   integrity sha512-8xOcRHvCjnocdS5cpwXQXVzmmh5e5+saE2QGoeQmbKmRS6J3VQppPOIt0MnmE+4xlZoumy0GPG0D0MVIQbNA1A==
 
-log-symbols@3.0.0:
-  version "3.0.0"
-  resolved "https://registry.yarnpkg.com/log-symbols/-/log-symbols-3.0.0.tgz#f3a08516a5dea893336a7dee14d18a1cfdab77c4"
-  integrity sha512-dSkNGuI7iG3mfvDzUuYZyvk5dD9ocYCYzNU6CYDE6+Xqd+gwme6Z00NS3dUh8mq/73HaEtT7m6W+yUPtU6BZnQ==
-  dependencies:
-    chalk "^2.4.2"
-
-log-symbols@^2.1.0:
+log-symbols@2.2.0, log-symbols@^2.1.0:
   version "2.2.0"
   resolved "https://registry.yarnpkg.com/log-symbols/-/log-symbols-2.2.0.tgz#5740e1c5d6f0dfda4ad9323b5332107ef6b4c40a"
   integrity sha512-VeIAFslyIerEJLXHziedo2basKbMKtTw3vfn5IzG0XTjhAVEJyNHnL2p7vc+wBDSdQuUpNw3M2u6xb9QsAY5Eg==
@@ -5308,17 +5301,17 @@ mkdirp@0.5.1:
   dependencies:
     minimist "0.0.8"
 
-mkdirp@0.5.3, mkdirp@^0.5.0, mkdirp@^0.5.1, mkdirp@~0.5.1:
+mkdirp@^0.5.0, mkdirp@^0.5.1, mkdirp@~0.5.1:
   version "0.5.3"
   resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-0.5.3.tgz#5a514b7179259287952881e94410ec5465659f8c"
   integrity sha512-P+2gwrFqx8lhew375MQHHeTlY8AuOJSrGf0R5ddkEndUkmwpgUob/vQuBD1V22/Cw1/lJr4x+EjllSezBThzBg==
   dependencies:
     minimist "^1.2.5"
 
-mocha@^7.0.0:
-  version "7.1.1"
-  resolved "https://registry.yarnpkg.com/mocha/-/mocha-7.1.1.tgz#89fbb30d09429845b1bb893a830bf5771049a441"
-  integrity sha512-3qQsu3ijNS3GkWcccT5Zw0hf/rWvu1fTN9sPvEd81hlwsr30GX2GcDSSoBxo24IR8FelmrAydGC6/1J5QQP4WA==
+mocha@7.0.1:
+  version "7.0.1"
+  resolved "https://registry.yarnpkg.com/mocha/-/mocha-7.0.1.tgz#276186d35a4852f6249808c6dd4a1376cbf6c6ce"
+  integrity sha512-9eWmWTdHLXh72rGrdZjNbG3aa1/3NRPpul1z0D979QpEnFdCG0Q5tv834N+94QEN2cysfV72YocQ3fn87s70fg==
   dependencies:
     ansi-colors "3.2.3"
     browser-stdout "1.3.1"
@@ -5331,9 +5324,9 @@ mocha@^7.0.0:
     growl "1.10.5"
     he "1.2.0"
     js-yaml "3.13.1"
-    log-symbols "3.0.0"
+    log-symbols "2.2.0"
     minimatch "3.0.4"
-    mkdirp "0.5.3"
+    mkdirp "0.5.1"
     ms "2.1.1"
     node-environment-flags "1.0.6"
     object.assign "4.1.0"
@@ -5341,8 +5334,8 @@ mocha@^7.0.0:
     supports-color "6.0.0"
     which "1.3.1"
     wide-align "1.1.3"
-    yargs "13.3.2"
-    yargs-parser "13.1.2"
+    yargs "13.3.0"
+    yargs-parser "13.1.1"
     yargs-unparser "1.6.0"
 
 module-deps@^6.0.0:
@@ -8130,7 +8123,15 @@ yallist@^2.1.2:
   resolved "https://registry.yarnpkg.com/yallist/-/yallist-2.1.2.tgz#1c11f9218f076089a47dd512f93c6699a6a81d52"
   integrity sha1-HBH5IY8HYImkfdUS+TxmmaaoHVI=
 
-yargs-parser@13.1.2, yargs-parser@^13.1.2:
+yargs-parser@13.1.1:
+  version "13.1.1"
+  resolved "https://registry.yarnpkg.com/yargs-parser/-/yargs-parser-13.1.1.tgz#d26058532aa06d365fe091f6a1fc06b2f7e5eca0"
+  integrity sha512-oVAVsHz6uFrg3XQheFII8ESO2ssAf9luWuAd6Wexsu4F3OtIW0o8IribPXYrD4WC24LWtPrJlGy87y5udK+dxQ==
+  dependencies:
+    camelcase "^5.0.0"
+    decamelize "^1.2.0"
+
+yargs-parser@^13.1.1, yargs-parser@^13.1.2:
   version "13.1.2"
   resolved "https://registry.yarnpkg.com/yargs-parser/-/yargs-parser-13.1.2.tgz#130f09702ebaeef2650d54ce6e3e5706f7a4fb38"
   integrity sha512-3lbsNRf/j+A4QuSZfDRA7HRSfWrzO0YjqTJd5kjAq37Zep1CEgaYmrH9Q3GwPiB9cHyd1Y1UwggGhJGoxipbzg==
@@ -8162,7 +8163,23 @@ yargs-unparser@1.6.0:
     lodash "^4.17.15"
     yargs "^13.3.0"
 
-yargs@13.3.2, yargs@^13.3.0:
+yargs@13.3.0:
+  version "13.3.0"
+  resolved "https://registry.yarnpkg.com/yargs/-/yargs-13.3.0.tgz#4c657a55e07e5f2cf947f8a366567c04a0dedc83"
+  integrity sha512-2eehun/8ALW8TLoIl7MVaRUrg+yCnenu8B4kBlRxj3GJGDKU1Og7sMXPNm1BYyM1DOJmTZ4YeN/Nwxv+8XJsUA==
+  dependencies:
+    cliui "^5.0.0"
+    find-up "^3.0.0"
+    get-caller-file "^2.0.1"
+    require-directory "^2.1.1"
+    require-main-filename "^2.0.0"
+    set-blocking "^2.0.0"
+    string-width "^3.0.0"
+    which-module "^2.0.0"
+    y18n "^4.0.0"
+    yargs-parser "^13.1.1"
+
+yargs@^13.3.0:
   version "13.3.2"
   resolved "https://registry.yarnpkg.com/yargs/-/yargs-13.3.2.tgz#ad7ffefec1aa59565ac915f82dccb38a9c31a2dd"
   integrity sha512-AX3Zw5iPruN5ie6xGRIDgqkT+ZhnRlZMLMHAs8tg7nRruy2Nb+i5o9bwghAogtM08q1dpr2LVoS8KSTMYpWXUw==