Fix issue with autoloading modules

[robertalexa]

@LukeTowers This is the code we looked at together.

The fix attempts (and seems to do the job) to fix the autoloading of modules packages.

[what-the-diff]

• Added a new line to the top of ServiceProvider.php
• Changed foreach loop in register() method from Config::get('cms.loadModules', []) to $modules variable which was declared on line 26