Incorrect is_null transformation

[mrpavlikov]

changing is_null($var) to (null === $var) is cool, but it does it wrong combining with exclamation mark

if (!is_null($var)) => if (!null === $var)

[MKCG]

@mrpavlikov I fixed this issue with my last commit in this repository along with some others : https://github.com/MKCG/phpfmt_7-1

Hope this help ;-)