Rename background option to backgroundColor for clarity

[sindresorhus]

When just reading the options in the code it's not immediately clear it's the background color. This would also better match the colors option.

[dominikwilkowski]

Mh 🤔 that would break the API and issue a new major version. Not sure if it's worth it. I keep it in the back of my mind and leave this issue open for others to add their perspectives.

[sindresorhus]

You don't have to make it a breaking change. I would just rename it and add an alias for background=>backgroundColor to preserve backward compatibility, and then remove the alias in the next major.

[dominikwilkowski]

Yeah I did just that. Let me know if you have issues.