[DayButton] when disabled will not update hover state

[mmaddex]

Problem description

Admittedly the use case involve using DatePicker internals individually.

Use case: I have a Calendar thats always visible, I disable the date when it's clicked, but then its left with the hover.

Playing around locally I resolved the issue by removing this conditional https://github.com/callemall/material-ui/blob/master/src/DatePicker/DayButton.js#L84

Link to minimal working code that reproduces the issue

Will update with an example, but webpackbin is giving me a

There are not any available packagers, we probably need to scale up, please let us know!

error right now

Versions

• Material-UI: 0.15.4
• React: 15.3.2
• Browser: Chrome 56.0.2924.87

Happy to submit a PR if you all would be receptive to this change.

[oliviertassinari]

Closing for #4787