Add babel-plugin-transform-object-assign to transform Object.assign

[nguquen]

Add babel-plugin-transform-object-assign to transform Object.assign in extendReactClass.js

[gajus]

Whats the reason?

[nguquen]

If not, it will throw Object doesn't support property or method "assign" on IE 11, and we got blank page on IE 11 or old browsers.

[gajus]

Polyfill-ing is not responsibility of react-css-modules.

Use https://polyfill.io/

[mirovelk]

Transforming Object.assign is not the same as polyfilling. There are situations when polyfill in browser can't be used (is not allowed).

By having Object.assign in your code you are disabling testing in phantomjs as well (where Object.assign is not supported as well).

Most libraries use https://www.npmjs.com/package/object-assign or https://www.npmjs.com/package/babel-plugin-transform-object-assign to prevent these issues.

[transplier]

One of the advantages of css-modules is isolation. Given this, it seems odd to require the mutation of the host environment (polyfilling) in order to use css-modules, especially in library scenarios.