Button should forward the ref to the material component

[stuarthendren]

Example issue from a storybook

Warning: Function components cannot be given refs. Attempts to access this ref will fail. Did you mean to use React.forwardRef()? 

Check the render method of `Styled(Component)`. 
    at http://localhost:6006/vendors~main.ab3ba32b17a7f0de2017.bundle.js:1290:16
    at Styled(Component) (http://localhost:6006/vendors~main.ab3ba32b17a7f0de2017.bundle.js:58034:28)
    at div
    at ThemeProvider (http://localhost:6006/vendors~main.ab3ba32b17a7f0de2017.bundle.js:56966:24)
    at ControlledThemeProvider (http://localhost:6006/vendors~main.ab3ba32b17a7f0de2017.bundle.js:3339:20)
    at ThemeController (http://localhost:6006/vendors~main.ab3ba32b17a7f0de2017.bundle.js:3295:71)
    at CustomThemeProvider
    at ThemeProvider
    at storyFn
    at ErrorBoundary