update color name replacement regex

currently in master, given the following css

```
#crazy{color:black;background-color:purple}
```

`black` and `purple` are matched as `:black;` and `purple}`, which means it gets transformed into

```
#crazy { color#000000background-color#800080
```

which causes rework to vomit

this pours pepto all over rework's tum tum