refactor: fix some coding style pointed by standard js

browser/main/modals/PreferencesModal/HotkeyTab.js

@@ -7,8 +7,6 @@ import store from 'browser/main/store'
 const electron = require('electron')
 const ipc = electron.ipcRenderer
 
-const OSX = global.process.platform === 'darwin'
-
 class HotkeyTab extends React.Component {
   constructor (props) {
     super(props)

browser/main/modals/PreferencesModal/InfoTab.js

@@ -1,4 +1,4 @@
-import React, { PropTypes } from 'react'
+import React from 'react'
 import CSSModules from 'browser/lib/CSSModules'
 import styles from './InfoTab.styl'
 

browser/main/modals/PreferencesModal/StorageItem.js

@@ -106,7 +106,10 @@ class UnstyledFolderItem extends React.Component {
     const popover = { position: 'absolute', zIndex: 2 }
     const cover = {
       position: 'fixed',
-      top: 0, right: 0, bottom: 0, left: 0
+      top: 0,
+      right: 0,
+      bottom: 0,
+      left: 0
     }
     const pickerStyle = Object.assign({}, {
       position: 'absolute'

browser/main/modals/PreferencesModal/UiTab.js

@@ -5,9 +5,6 @@ import ConfigManager from 'browser/main/lib/ConfigManager'
 import store from 'browser/main/store'
 import consts from 'browser/lib/consts'
 
-const electron = require('electron')
-const ipc = electron.ipcRenderer
-
 const OSX = global.process.platform === 'darwin'
 
 class UiTab extends React.Component {