sequencer.c: plug mem leak in git_sequencer_config

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: stefanbeller

sequencer.c

@@ -174,6 +174,7 @@ static int git_sequencer_config(const char *k, const char *v, void *cb)
 			warning(_("invalid commit message cleanup mode '%s'"),
 				  s);
 
+		free((char *)s);
 		return status;
 	}