Fix ESLint warnings that appeared after running auto-formatting

`// eslint-disable-line` magic comments got moved down a line so they no
longer referred to the intended code. Switch to using
`// eslint-disable-next-line` instead.

src/shared/discovery.js

@@ -203,6 +203,7 @@ class Discovery {
       }
     } else {
       // Handle message as a client frame.
+      // eslint-disable-next-line no-lonely-if
       if (messageType === 'offer') {
         // eslint-disable-line no-lonely-if
         if (!this.requestInProgress) {

src/sidebar/components/test/annotation-header-test.js

@@ -29,8 +29,8 @@ describe('sidebar.components.annotation-header', function() {
   beforeEach('Import and register the annotationHeader component', function() {
     const annotationHeader = proxyquire('../annotation-header', {
       '../annotation-metadata': {
+        // eslint-disable-next-line no-unused-vars
         domainAndTitle: function(ann) {
-          // eslint-disable-line no-unused-vars
           return fakeDocumentMeta;
         },
       },

src/sidebar/render-markdown.js

@@ -44,8 +44,8 @@ function extractMath(content) {
   let pos = 0;
   let replacedContent = content;
 
+  // eslint-disable-next-line no-constant-condition
   while (true) {
-    // eslint-disable-line no-constant-condition
     const blockMathStart = replacedContent.indexOf('$$', pos);
     const inlineMathStart = replacedContent.indexOf('\\(', pos);