Use an absolute path for files from the process root so that ES6 module import statements work correctly.

Author: ChadKillingsworth

lib/gulp/concat-to-json.js

@@ -44,11 +44,12 @@ function json_file(src, path, source_map) {
  * @return {string}
  */
 module.exports = function(files) {
+  var path = require('path');
   var jsonFiles = [];
   for (var i = 0; i < files.length; i++) {
     jsonFiles.push(
         json_file(files[i].contents.toString(),
-            files[i].relative,
+            '/' + path.relative(process.cwd(), files[i].path),
             files[i].sourceMap ? JSON.stringify(files[i].sourceMap) : undefined));
   }