Upgrade symfony/process

[ghost]

All of the underlying Symfony components used by Laravel 5.6 have been upgraded to the Symfony ^4.0 release series.

[james-nesbitt]

this is in ambition a duplicate of #880

#880 is farther ahead in terms of repercusions of updating symfony/process

[glensc]

this is identical to #866, so I think this one should be closed as a duplicate.

[LukeTowers]

This has been implemented in the 2.0 branch of assetic-php/assetic. Until we tag 2.0, you can pull it in by using "assetic/framework": "dev-2.0/dev" in your composer.json files.