Disable case value-keyword-case for composes

[pascalduez]

See #7, #13

Just checking what it takes, whether it make sense or not.

While this "solves" the issue with classes used with composes. This does not solve the one with @value.

@value camelCase: green;
a { color: camelCase } /* error */

Since @value can be used in a wide range of properties, we don't have much solutions here.

Also we can see that disabling selector-class-pattern was necessary locally.
The CSS modules spec don't enforce a particular case, so this config won't disable selector-class-pattern. It's out of scope.

The whole benefit of this change is quite debatable, some per projects overrides will always be needed.
One would still need to:

• disable selector-class-pattern locally
• change case for @value or build a unmaintainable list of ignored properties