removed deprecated UnitTest framework and added missing Test import in mockito.dart

Author: Stephen Turley

lib/mockito.dart

@@ -1,6 +1,7 @@
 library mockito;
 
 import 'package:matcher/matcher.dart';
+import 'package:test/test.dart';
 import 'dart:mirrors';
 
 bool _whenInProgress = false; 

test/mockitoSpec.dart

@@ -1,4 +1,4 @@
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 import '../lib/mockito.dart';
 
 class RealClass {