Add <GoogleAnalytics /> component

src/components/GoogleAnalytics.js

@@ -0,0 +1,16 @@
+import React from 'react'
+import { Route } from 'react-router-dom'
+
+export default () => (
+  <Route
+    path='/'
+    render={({ location }) => {
+      // Assumes google analytics code already added to index.html
+      if (typeof window.ga === 'function') {
+        window.ga('set', 'page', location.pathname + location.search)
+        window.ga('send', 'pageview')
+      }
+      return null
+    }}
+  />
+)