Update merge-request-event.json

apply go-playground#99

Author: lsascha

testdata/gitlab/merge-request-event.json

@@ -108,8 +108,14 @@
     "group_id": 41
   }],
   "changes": {
-    "updated_by_id": [null, 1],
-    "updated_at": ["2017-09-15 16:50:55 UTC", "2017-09-15 16:52:00 UTC"],
+    "updated_by_id": {
+      "previous": null,
+      "current": 1
+    },
+    "updated_at": {
+      "previous": "2017-09-15 16:50:55 UTC",
+      "current":"2017-09-15 16:52:00 UTC"
+    },
     "labels": {
       "previous": [{
         "id": 206,
@@ -137,4 +143,4 @@
       }]
     }
   }
-}
+}