moved actual grunt file to build dir

Gruntfile.js

@@ -1,5 +1,7 @@
 require('babel/register');
 
+// Need to `require` a separate Grunt file so we can use ES6 syntax via
+// Babel's require hook.
 module.exports = function(grunt) {
-  require('./grunt.js')(grunt);
+  require('./build/grunt.js')(grunt);
 };