Devtools: Fix mock-file filter function

Author: mdtusz

devtools/test_dashboard/server.js

@@ -74,7 +74,9 @@ function readFiles(files) {
 function createMocksList(files) {
 
     // eliminate pollutants (e.g .DS_Store) that can accumulate in the mock directory
-    var jsonFiles = files.filter(function(file) {return file.extname === '.json';});
+    var jsonFiles = files.filter(function(file) {
+        return file.name.substr(-5) === '.json';
+    });
 
     var mocksList = jsonFiles.map(function(file) {
         var contents = JSON.parse(file.contents);