Update CONTRIBUTING.md (fix dead link)
Update CONTRIBUTING.md (fix dead link)

zephir-lang/zephir,zephir-lang/zephir,phalcon/zephir,phalcon/zephir,vpg/zephir,zephir-lang/zephir,vpg/zephir,phalcon/zephir,vpg/zephir,phalcon/zephir,vpg/zephir,vpg/zephir,vpg/zephir,phalcon/zephir,phalcon/zephir,zephir-lang/zephir,zephir-lang/zephir