Add specs for modified color module functions


- [ ] color.invert() (a wip PR has [been started](https://github.com/oddbird/sass-spec/pull/7))
- [ ] color.hwb()[deprecated]
- [ ] color.change()
- [ ] color.adjust()
- [ ] color.scale()
- [ ] color.ie-hex-str()


See https://github.com/sass/sass/issues/2831