Fix environment variable not being interpreted as string.

lib/components/App.js

@@ -94,7 +94,7 @@ export default class App extends React.Component {
             </p>
           </footer>
           <script>FilePizza()</script>
-          { process.env.DISABLE_GA != 'yes' && <ga.Initializer /> }
+          { process.env.DISABLE_GA != 'yes' ? <ga.Initializer /> : <div></div> }
         </body>
       </html>
     );

webpack.config.js

@@ -30,7 +30,7 @@ module.exports = {
   plugins: [
     new webpack.DefinePlugin({
       'process.env': {
-        'DISABLE_GA': process.env.DISABLE_GA,
+        'DISABLE_GA': JSON.stringify(process.env.DISABLE_GA),
       }
     })
   ],