Fix test failures when arrow functions are not transformed

Native (non-transpiled) arrow functions cannot be used with the `new` operator.
This commit fixes a couple of cases where that was happening.

src/annotator/plugin/test/pdf-test.js

@@ -45,7 +45,7 @@ describe('annotator/plugin/pdf', () => {
     };
 
     $imports.$mock({
-      './pdf-metadata': () => fakePDFMetadata,
+      './pdf-metadata': sinon.stub().returns(fakePDFMetadata),
       '../anchoring/pdf': fakePdfAnchoring,
 
       // Disable debouncing of updates.

src/shared/test/injector-test.js

@@ -66,7 +66,7 @@ describe('Injector', () => {
 
       container.register('foo', fooFactory);
       container.register('bar', barFactory);
-      container.register('baz', bazFactory);
+      container.register('baz', { factory: bazFactory });
 
       const baz = container.get('baz');
       assert.equal(baz.foo, foo);

src/sidebar/services/test/oauth-auth-test.js

@@ -78,7 +78,7 @@ describe('sidebar/services/oauth-auth', function () {
       authorize: sinon.stub().returns(Promise.resolve(null)),
     };
 
-    FakeOAuthClient = config => {
+    FakeOAuthClient = function (config) {
       fakeClient.config = config;
       return fakeClient;
     };

yarn.lock

@@ -154,7 +154,7 @@
   dependencies:
     "@babel/types" "^7.12.1"
 
-"@babel/helper-module-imports@^7.10.4", "@babel/helper-module-imports@^7.12.1":
+"@babel/helper-module-imports@^7.12.1":
   version "7.12.1"
   resolved "https://registry.yarnpkg.com/@babel/helper-module-imports/-/helper-module-imports-7.12.1.tgz#1644c01591a15a2f084dd6d092d9430eb1d1216c"
   integrity sha512-ZeC1TlMSvikvJNy1v/wPIazCu3NdOwgYZLIkmIyAsGhqkNpiDoQQRmaCK8YP4Pq3GPTLPV9WXaPCJKvx06JxKA==