Enforce coding standards.

[raphaelstolt]

Adds a local php-cs-fixer cache and validation during Travis CI builds.

[localheinz]

Unfortunately, the caching doesn't work on Travis, but if you dare to use friendsofphp/php-cs-fixer:v2.0.0-alpha, then you can make use of it on Travis, too!

This significantly speeds up build times.

For an example, take a look at https://github.com/refinery29/php-cs-fixer-config/blob/master/.php_cs!

We have been using it for a while, it works fine.

On a separate note, I can't wait for 2.0.0 release of friendsofphp-php-cs-fixer!

😄

For reference, see PHP-CS-Fixer/PHP-CS-Fixer#1076.

[raphaelstolt]

@localheinz Thanks for the heads-up. I guess we wait for the 2.0.0 release of friendsofphp-php-cs-fixer, or @jonathantorres should we go experimentell?

[jonathantorres]

I wouldn't mind using the alpha version on the construct codebase itself. For the generated project we should use the 2.0.0 release.

[raphaelstolt]

Done with #151. We should prolly create a backlog issue to update the generated project artifacts once 2.0.0 is released.