Fix read of .env variables (facebook#2242)

Author: ApacheEx

config/env.js

@@ -13,6 +13,9 @@
 const fs = require('fs');
 const paths = require('./paths');
 
+// Make sure that including paths.js after env.js will read .env variables.
+delete require.cache[require.resolve('./paths')];
+
 const NODE_ENV = process.env.NODE_ENV;
 if (!NODE_ENV) {
   throw new Error(