cvsserver: Remove trailing "\n" from commithash in checkin function

cvsserver: Remove trailing "\n" from commithash in checkin function

The commithash for updating the ref is obtained from a call to
git-commit-tree.  However, it was returned (and stored) with the
trailing newline.  This meant that the later call to git-update-ref that
was trying to update to $commithash was including the newline in the
parameter - obviously that hash would never exist, and so git-update-ref
would always fail.

The solution is to chomp() the commithash as soon as it is returned by
git-commit-tree.

Signed-off-by: Andy Parkins <andyparkins@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>