Unleash eslint on models/messages.js

Fun fact: eslint was not running on this file, despite the eslint
directives previously in the file!

.eslintignore

@@ -22,6 +22,7 @@ ts/**/*.js
 !js/database.js
 !js/logging.js
 !js/models/conversations.js
+!js/models/messages.js
 !js/views/attachment_view.js
 !js/views/conversation_search_view.js
 !js/views/backbone_wrapper_view.js

Gruntfile.js

@@ -112,6 +112,7 @@ module.exports = function(grunt) {
         '!js/views/debug_log_view.js',
         '!js/views/message_view.js',
         '!js/models/conversations.js',
+        '!js/models/messages.js',
         '!js/WebAudioRecorderMp3.js',
         '!libtextsecure/message_receiver.js',
         '_locales/**/*'