check for directory existence when storing console log or storing source, if it does not exist create it

[ssanko]

This PR fixes missing destination directory for storing console log or source code.

Currently when saving console log or source code to the path defined in \Laravel\Dusk\Browser::$storeConsoleLogAt or \Laravel\Dusk\Browser::$storeSourceAt, the code does not check for the existence of the directory.

Because of missing check for destination directory existence, current code throws ErrorException when trying to save console log or source code:

file_put_contents(/Sites/laravel-dusk/storage/app/customPath/pageSources/source.txt): Failed to open stream: No such file or directory

This PR adds code to check for the exitence of the destination directory and if it does not exist, then tries to create it.

[taylorotwell]

Any reason why you use 0777 permissions instead of 0755?

[ssanko]

I wanted to stick to the logic used in method \Laravel\Dusk\Browser::screenshotElement which uses the 0777 permission.

So if the 0755 is more reasonable, then I'll change the permissions also for \Laravel\Dusk\Browser::screenshotElement method.