fmt-merge-msg: fix coding style

Align argument list and place opening brace on its own line.

Signed-off-by: Dimitrios Christidis <dimitrios@christidis.me>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fmt-merge-msg.c

@@ -407,7 +407,8 @@ static void shortlog(const char *name,
 }
 
 static void fmt_merge_msg_title(struct strbuf *out,
-	const char *current_branch) {
+				const char *current_branch)
+{
 	int i = 0;
 	char *sep = "";