Drop unneeded .js extensions

lib/renderer/chrome-api.js

@@ -161,7 +161,7 @@ exports.injectTo = function (extensionId, isBackgroundPage, context) {
     onMessage: chrome.runtime.onMessage
   }
 
-  chrome.storage = require('./extensions/storage.js')
+  chrome.storage = require('./extensions/storage')
 
   chrome.pageAction = {
     show () {},
@@ -173,6 +173,6 @@ exports.injectTo = function (extensionId, isBackgroundPage, context) {
     getPopup () {}
   }
 
-  chrome.i18n = require('./extensions/i18n.js').setup(extensionId)
-  chrome.webNavigation = require('./extensions/web-navigation.js')
+  chrome.i18n = require('./extensions/i18n').setup(extensionId)
+  chrome.webNavigation = require('./extensions/web-navigation')
 }