git-browser: update to latest

git-browser: update to latest

Previous versions of git-browser did some bad things
mucking about with GIT_EXEC_PATH and passing paths and
variables to ls-remote as part of the --upload-pack
argument.

Starting with Git 2.5.0, git is a little bit less
forgiving and some broken things that should never have
worked in the first place stopped working.

Pick up the newest version of git-browser.cgi to
avoid these nasty incompatibilities.

The new version also includes a change to show HEAD
in the listing so that in case HEAD is detached and
there are no other refs under refs/heads/ or refs/tags/
a listing can still be displayed.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>