Tidy whitespace and remove duplicates

[bradlc]

This PR adds a couple of additional class list formatting features to the plugin:

1. Whitespace tidying. Excess whitespace is removed from single-line class lists:

   - <div className="    sm:p-0   p-4  " />
   + <div className="p-4 sm:p-0" />

2. Duplicate removal. Duplicate classes are removed from class lists:

   - <div className="sm:p-0 p-4 p-4" />
   + <div className="p-4 sm:p-0" />

[hyunbinseo]

Link for this PR in the v0.1.9 release is incorrect.

[ruoruochen]

Why doesn't it work here? "prettier-plugin-tailwindcss": "^0.1.13",