Update React Helmet import (decaporg#244)

Author: helau64

src/components/Layout.js

@@ -1,5 +1,5 @@
 import React from 'react'
-import Helmet from 'react-helmet'
+import { Helmet } from 'react-helmet'
 import Footer from '../components/Footer'
 import Navbar from '../components/Navbar'
 import './all.sass'