Fix a dartdoc typo (#47)

diff --git a/lib/src/core_matchers.dart b/lib/src/core_matchers.dart
index 3ecbb9d..c75739d 100644
--- a/lib/src/core_matchers.dart
+++ b/lib/src/core_matchers.dart
@@ -361,7 +361,7 @@
 }
 
 /// Returns a matcher that matches if an object is an instance
-/// of [type] (or a subtype).
+/// of [T] (or a subtype).
 ///
 /// As types are not first class objects in Dart we can only
 /// approximate this test by using a generic wrapper class.