Radio button triggers onChange instead of OnCheck

The radio button class has some confusion on what events it is supposed to export and trigger.  I opted to use the onChange event because the radiobtn module was already exporting it, but if you prefer onCheck that would be fine too.

On a related note, the docs at http://gumbyframework.com/docs/javascript/#!/events-initialization use Gumby.onChange (with a capital G), but I think the ui modules are using gumby with a lowercase g.

I made this edit on a modified fork of gumby and just thought I'd toss the pull request out there to raise awareness of these differences, feel free to close this request if needed.