Bugfix: fixed call to renamed function pla_password_hash.

I was receiving the following error when I created a new user with md5crypt passwords and using php55-5.5.10
E_WARNING: password_hash() expects parameter 2 to be long, string given

I noticed the function password_hash was renamed to pla_password_hash because php55 has a internal function named password_hash. I believe the file lib/PageRender.php was not updated after renaming the pla_password_hash function. At my environment this change fixed the issue.

BTW: Tnx for maintaining the code at github!