Modify shebang to be more portable (#3038)

The new shebang is a portable way to find the php interpreter. It works
on Mac, GNU/Linux and BSD.

cli/create-user.php

@@ -1,4 +1,4 @@
-#!/usr/bin/php
+#!/usr/bin/env php
 <?php
 $isUpdate = false;
 require(__DIR__ . '/_update-or-create-user.php');