changed twoItemSwitcher text to black to make the options visible

[andrewkoung]

fixes #33

[joelwass]

@andrewkoung Can we make this a prop instead of hardcoding? it looks like there will be different use cases for the switcher component having different letter colors

something like:

className={switcher__leftItem ${props.color} `

and then passing in color="black" or color="white" in the parent components wherever it's used

[stripedpajamas]

@joelwass wouldn't that mean we'd necessarily need to write a color-class when passing a color into this component? I don't like the idea of having another piece of the project (scss file) be an indirect dependency of this component. How about we make a color prop directly alter the style and we can drop the class-colors.

[andrewkoung]

I've created a color prop in my latest push. Is this fine?