Use tab character in HardTabs pre-commit hook

Turns out some systems don't support `\t` as an escape sequence. This
was resulting one spec failing for this hook.

Changing it to a literal tab solves the problem.

Change-Id: If4d50b64d2d341cb673cd1bb7c54f8841729b21d
Reviewed-on: http://gerrit.causes.com/35626
Reviewed-by: Shane da Silva <shane@causes.com>
Tested-by: Shane da Silva <shane@causes.com>