Add `operator-linebreak` ESLint rule

Based on the following discussion:
https://github.com/signalapp/Signal-Desktop/pull/2040#discussion_r168029106

.eslintrc.js

@@ -37,5 +37,7 @@ module.exports = {
 
     // though we have a logger, we still remap console to log to disk
     'no-console': 'off',
+
+    'operator-linebreak': ["error", "after", { "overrides": { '?': 'before', ':': 'before' } }]
   }
 };

app/logging.js

@@ -117,8 +117,8 @@ function eliminateOutOfDateFiles(logPath, date) {
       const file = {
         path: target,
         start: isLineAfterDate(start, date),
-        end: isLineAfterDate(end[end.length - 1], date)
-          || isLineAfterDate(end[end.length - 2], date),
+        end: isLineAfterDate(end[end.length - 1], date) ||
+             isLineAfterDate(end[end.length - 2], date),
       };
 
       if (!file.start && !file.end) {

js/background.js

@@ -518,9 +518,9 @@
       return ev.confirm();
     }
 
-    const { type, id } = data.message.group ?
-      { type: 'group', id: data.message.group.id } :
-      { type: 'private', id: data.source };
+    const { type, id } = data.message.group
+      ? { type: 'group', id: data.message.group.id }
+      : { type: 'private', id: data.source };
 
     const processedMessage = await Message.process(data.message);
 

js/views/file_input_view.js

@@ -206,9 +206,9 @@
       if (file === undefined) {
         return Promise.resolve();
       }
-      const attachmentFlags = this.isVoiceNote ?
-        textsecure.protobuf.AttachmentPointer.Flags.VOICE_MESSAGE :
-        null;
+      const attachmentFlags = this.isVoiceNote
+        ? textsecure.protobuf.AttachmentPointer.Flags.VOICE_MESSAGE
+        : null;
 
       const setFlags = flags => (attachment) => {
         const newAttachment = Object.assign({}, attachment);

main.js

@@ -157,10 +157,10 @@ function isVisible(window, bounds) {
   const topClearOfUpperBound = window.y >= boundsY;
   const topClearOfLowerBound = (window.y <= (boundsY + boundsHeight) - BOUNDS_BUFFER);
 
-  return rightSideClearOfLeftBound
-    && leftSideClearOfRightBound
-    && topClearOfUpperBound
-    && topClearOfLowerBound;
+  return rightSideClearOfLeftBound &&
+    leftSideClearOfRightBound &&
+    topClearOfUpperBound &&
+    topClearOfLowerBound;
 }
 
 function createWindow() {
@@ -277,8 +277,8 @@ function createWindow() {
   // Emitted when the window is about to be closed.
   mainWindow.on('close', (e) => {
     // If the application is terminating, just do the default
-    if (windowState.shouldQuit()
-      || config.environment === 'test' || config.environment === 'test-lib') {
+    if (windowState.shouldQuit() ||
+        config.environment === 'test' || config.environment === 'test-lib') {
       return;
     }
 
@@ -422,9 +422,9 @@ app.on('before-quit', () => {
 app.on('window-all-closed', () => {
   // On OS X it is common for applications and their menu bar
   // to stay active until the user quits explicitly with Cmd + Q
-  if (process.platform !== 'darwin'
-    || config.environment === 'test'
-    || config.environment === 'test-lib') {
+  if (process.platform !== 'darwin' ||
+      config.environment === 'test' ||
+      config.environment === 'test-lib') {
     app.quit();
   }
 });