include plugin tests

Change-Id: Ief5d156fb856f3d63bc0c1fb0c669c0f7cdda9d8
diff --git a/Makefile.PL b/Makefile.PL
index 1b52abc..bc71cd6 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -62,6 +62,6 @@
   },
 
   test => {
-    TESTS => 't/*.t'
+    TESTS => 't/*.t t/plugin/*.t'
   }
 );