Add test-run-command to .gitignore

Add test-run-command to .gitignore so it does not pollute
git status output.

Signed-off-by: Alejandro Riveira Fernández <ariveira@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -166,6 +166,7 @@
 /test-match-trees
 /test-parse-options
 /test-path-utils
+/test-run-command
 /test-sha1
 /test-sigchain
 /common-cmds.h