Fix git chmod alias

This command previously would only work from the root directory of the
repository. This commit updates it to work properly when run for files
deeper in the directory tree.

src/.gitconfig

@@ -7,7 +7,7 @@
 	alias = !git config -l | grep '^alias\\.' | cut -d '.' -f '2-' | sed -r -e 's/=/ = /' | sort
 	amend = commit --amend
 	amend-a = commit -a --amend
-	chmod = "!f() { chmod_flag=$1 && shift && git add --chmod=$chmod_flag $@ && chmod $chmod_flag $@; }; f"
+	chmod = "!f() { chmod_flag=$1 && shift && cd -- \"${GIT_PREFIX:-.}\"; git add --chmod=\"$chmod_flag\" \"$@\" && chmod \"$chmod_flag\" \"$@\"; }; f"
 	# TODO: fix below; that method is not accurate
 #	check-merge = "!f() { output=$(git format-patch ${1:-master} --stdout | git apply --3way --check - 2>/dev/null); exit_code=$?; if [ $exit_code != '0' ] && [ $exit_code != '128' ]; then echo 'Merge conflicts exist! See `git apply` output below:'; echo; echo $output; fi; }; f"
 	co-pr = "!f() { \