Update CONTRIBUTING.md

Fixed typo.
Killed captcha. Fixes #7

Signed-off-by: Robin van Baalen <robin@neverwoods.com>
Fixes #11

Signed-off-by: Robin van Baalen <robin@neverwoods.com>
Fixes #13 and #8
Merge remote branch 'origin/master' into wip-new-documentation

Fixed Conflicts:
	classes/ValidFormBuilder/Captcha.php
	classes/ValidFormBuilder/ValidForm.php