message: change Button back to "is"
diff: @@ -10,8 +10,8 @@ describe('Button', () => {
  expect(render(<Button />).type).toEqual('button')
  })
  - it('respects the "as" prop', () => {
  - expect(render(<Button as="a" />).type).toEqual('a')
  + it('respects the "is" prop', () => {
  + expect(render(<Button is="a" />).type).toEqual('a')
  })
  it('implements common system props', () => {
  