composer: fix warning

[StyXman]

Fixes #1118

[jtojnar]

Thank you for the pull request. We are soon going to merge #1096, which removes CSSMin, making this issue moot.

Also note that when you update composer.json it is a good practice to run composer update --lock to propagate the changes to the composer.lock file.

[StyXman]

when you update composer.json it is a good practice to run composer update --lock to propagate the changes to the composer.lock file.

Heh, I didn't know, sorry, I'm far from being a PHP dev. Closing, then...

[jtojnar]

I guess we can merge it in the meanwhile. Thanks for the PR.