strbuf: clarify dependency

refs.h was once needed but is no longer so as of 6bab74e ("strbuf:
move strbuf_branchname to sha1_name.c", 2010-11-06). strbuf.h was
included thru refs.h, so removing refs.h requires strbuf.h to be added
back.

Signed-off-by: Calvin Wan <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: calvin-wan-google

strbuf.c

@@ -5,8 +5,8 @@
 #include "gettext.h"
 #include "hex.h"
 #include "object-name.h"
-#include "refs.h"
 #include "repository.h"
+#include "strbuf.h"
 #include "string-list.h"
 #include "utf8.h"
 #include "date.h"