fix HMR (#680)

Author: nkzawa

client/next-dev.js

@@ -1,4 +1,3 @@
-import 'react-hot-loader/patch'
 import patch from './patch-react'
 
 // apply patch first
@@ -7,5 +6,7 @@ patch((err) => {
   next.renderError(err)
 })
 
+require('react-hot-loader/patch')
+
 const next = require('./next')
 window.next = next