**Do you want to request a *feature* or report a *bug*?**

Bug

### Current Behaviour

 - `ReactDOMServer.renderToString` is mutating CSS Variable names that are inlined and in the `--camelCase` format into `--kebab-case`

### Expected Behaviour

 - `ReactDOMServer.renderToString` does not mutate the CSS Variable name, and keeps it in `--camelCase` format

### Demo

 - https://codesandbox.io/s/react-dom-server-debugging-28xsr

### Versions:

 - Issue appears in `react@16.8.6` &  `react-dom@16.8.6` 
 - Issue appears in `react@16.0.0` & `react-dom@16.0.0` 
 - (That's all I've tested so far)

### Other notes:

 - It's worth noting that `ReactDOM.render` is preserving the CSS Variable name and not mutating it. It only seems to only be an issue with `ReactDOMServer.renderToString`

if (typeof Component.getDerivedStateFromProps !== 'function') {
          inst.componentWillMount();
        }
      }
      if (
        typeof inst.UNSAFE_componentWillMount === 'function' &&
        typeof Component.getDerivedStateFromProps !== 'function'
      ) {
        
        
        inst.UNSAFE_componentWillMount();
      }
      if (queue.length) {
        let oldQueue = queue;
        let oldReplace = replace;
        queue = null;
        replace = false;
        if (oldReplace && oldQueue.length === 1) {
          inst.state = oldQueue[0];
        } else {
          let nextState = oldReplace ? oldQueue[0] : inst.state;
          let dontMutate = true;
          for (let i = oldReplace ? 1 : 0; i < oldQueue.length; i++) {
            let partial = oldQueue[i];
            let partialState =
              typeof partial === 'function'
                ? partial.call(inst, nextState, element.props, publicContext)
                : partial;
            if (partialState != null) {
              if (dontMutate) {