Fix build (#95)

Analysis error reported here:
https://travis-ci.org/google/file.dart/jobs/399227998
diff --git a/packages/file/test/record_replay_matchers.dart b/packages/file/test/record_replay_matchers.dart
index 7a3b2f1..34c5387 100644
--- a/packages/file/test/record_replay_matchers.dart
+++ b/packages/file/test/record_replay_matchers.dart
@@ -584,7 +584,7 @@
   }
 }
 
-class _NoMatchingInvocationError extends TypeMatcher {
+class _NoMatchingInvocationError extends TypeMatcher<dynamic> {
   const _NoMatchingInvocationError() : super("NoMatchingInvocationError");
 
   @override