fix(dartdocs): Hide duplicate exports from guinness.

Duplicate exports were breaking dartdoc builds.

Closes https://github.com/angular/angular/issues/2072.

modules/angular2/src/test_lib/test_lib.dart

@@ -2,7 +2,16 @@ library test_lib.test_lib;
 
 import 'package:guinness/guinness.dart' as gns;
 export 'package:guinness/guinness.dart'
-    hide Expect, expect, NotExpect, beforeEach, it, iit, xit;
+    hide
+        Expect,
+        expect,
+        NotExpect,
+        beforeEach,
+        it,
+        iit,
+        xit,
+        SpyObject,
+        SpyFunction;
 import 'package:unittest/unittest.dart' hide expect;
 
 import 'dart:async';