Remove React, PureComponent global import, added those imports to files directly

• Remove:
- React, PureComponent global import and added those imports to files directly

app/javascript/gabsocial/containers/gabsocial.js

@@ -1,5 +1,6 @@
 'use strict'
 
+import React from 'react'
 import { Provider } from 'react-redux'
 import configureStore from '../store/configureStore'
 import { BrowserRouter, Route } from 'react-router-dom'
@@ -36,7 +37,7 @@ const mapStateToProps = (state) => ({
 })
 
 @connect(mapStateToProps)
-class GabSocialMount extends PureComponent {
+class GabSocialMount extends React.PureComponent {
 
   static propTypes = {
     shownOnboarding: PropTypes.bool.isRequired,
@@ -80,7 +81,7 @@ class GabSocialMount extends PureComponent {
 
 }
 
-export default class GabSocial extends PureComponent {
+export default class GabSocial extends React.PureComponent {
 
   static propTypes = {
     locale: PropTypes.string.isRequired,