Add posibility to style the knob itself. about react-toggle

[gfazioli]

@padsbanger hey, if you are using the styled-components, you may

const Wire = styled(Toggle)`
  && {
    input[type="checkbox"] + label::after {
      border:2px solid #000;
      width: 14px;
      height: 14px;
    }
  }  
`

and then

     <Label htmlFor="toggle-9">
            <Wire
              leftBackgroundColor="white"
              rightBackgroundColor="white"
              borderColor="black"
              knobColor="white"
              name="toggle-9"
              onToggle={e => console.log("onToggle", e.target.checked)}
            />
            Right label
   </Label>