Upgrade ESLint to v2

This commit also tweak the code style following backward-incompatible v2 rules.

client/lib/cssEvents.js

@@ -15,6 +15,7 @@ function whichTransitionEvent() {
       return transitions[t];
     }
   }
+  return null;
 }
 
 function whichAnimationEvent() {
@@ -32,6 +33,7 @@ function whichAnimationEvent() {
       return transitions[t];
     }
   }
+  return null;
 }
 
 CSSEvents = {

client/lib/escapeActions.js

@@ -64,6 +64,7 @@ EscapeActions = {
   clickExecute(target, maxLabel) {
     if (this._nextclickPrevented) {
       this._nextclickPrevented = false;
+      return false;
     } else {
       return this._execute({
         maxLabel,

client/lib/multiSelection.js

@@ -109,12 +109,11 @@ MultiSelection = {
 
   toggleRange(cardId) {
     const selectedCards = this._selectedCards.get();
-    let startRange;
     this.reset();
     if (!this.isActive() || selectedCards.length === 0) {
       this.toggle(cardId);
     } else {
-      startRange = selectedCards[selectedCards.length - 1];
+      const startRange = selectedCards[selectedCards.length - 1];
       this.toggle(getCardsBetween(startRange, cardId));
     }
   },

client/lib/popup.js

@@ -38,7 +38,8 @@ window.Popup = new class {
       if (self.isOpen()) {
         const previousOpenerElement = self._getTopStack().openerElement;
         if (previousOpenerElement === evt.currentTarget) {
-          return self.close();
+          self.close();
+          return;
         } else {
           $(previousOpenerElement).removeClass('is-active');
         }

client/lib/textComplete.js

@@ -14,6 +14,7 @@ $.fn.escapeableTextComplete = function(strategies, options, ...otherArgs) {
         evt.stopPropagation();
         return commands.KEY_ENTER;
       }
+      return null;
     },
     ...options,
   };