Correct shebang line for contrib/stats/packinfo.pl

"/bin/perl"?  What was I thinking?
Signed-off-by: NBrian Downing <bdowning@lavos.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

contrib/stats/packinfo.pl

-#!/bin/perl
+#!/usr/bin/perl
 #
 # This tool will print vaguely pretty information about a pack.  It
 # expects the output of "git-verify-pack -v" as input on stdin.