Add command tests to Makefile

Change-Id: I613ef10137d01a0d013e13fd6f612a0aee762098
diff --git a/Makefile.PL b/Makefile.PL
index bc71cd6..90f76a1 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -62,6 +62,6 @@
   },
 
   test => {
-    TESTS => 't/*.t t/plugin/*.t'
+    TESTS => 't/*.t t/plugin/*.t t/command/*.t'
   }
 );