Change the executable to allow different paths

For me PHP is installed in `/usr/bin/php` not `/usr/local/bin/php`
* https://thomashunter.name/blog/creating-self-executable-php-scripts/

sourcetree-merge-request-opener

@@ -1,4 +1,4 @@
-#!/usr/local/bin/php
+#!/usr/bin/env php
 <?php
 
 foreach (array(__DIR__ . '/../../autoload.php', __DIR__ . '/../vendor/autoload.php', __DIR__ . '/vendor/autoload.php') as $file) {