fix(generate): Replace + with \x00

[benmvp]

Problem

This PR changed the content being passed to interpolateName (in loader-utils) from including a plus + to including \x00. This is now in css-loader >= 4. However, generic-names still using + so there's now an inconsistency in how the class names are generated.

Given that this library is basically piggybacking on what webpack does, it should be updated to match.

This caused babel-plugin-react-css-modules to break: gajus/babel-plugin-react-css-modules#291

Solution

Use \x00 instead of + and update the tests.

Fixes #8.

BREAKING CHANGE: This change will result in new names being generated, particularly those using [hash]. You will need to upgrade to css-loader >= 4 if you are wanting to keep the classes in sync.