Missing font weight Semibold (600)

We're missing the font weight Semibold = 600

- `@freenow/wave` version: latest

### Relevant code

```js
fontWeight: 'semibold' // not working
```

### What was expected to happen?

It should render the text with `font-weight:600` but is bolder than it should
**Expected size:**

### Reproduction

If you can, try to reproduce the issue in a Codesandbox. You can fork the one
here: https://codesandbox.io/s/wave-playground-forked-fcv8tm?file=/src/App.js