ls-tree: cleanup the redundant SPACE

An redundant space was found in ls-tree.c, which is no doubt
a small change, but it might be OK to make a commit on its own.

Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/ls-tree.c

@@ -14,7 +14,7 @@
 #include "parse-options.h"
 #include "pathspec.h"
 
-static const  char * const ls_tree_usage[] = {
+static const char * const ls_tree_usage[] = {
 	N_("git ls-tree [<options>] <tree-ish> [<path>...]"),
 	NULL
 };