Add rollup-plugin-json

[chrisdothtml]

Currently, if you try to import a json file (e.g. package.json), you'll get an error:

SyntaxError: [...]/package.json: Unexpected token, expected ";" (2:8)
  1 | {
  2 |   "name": "foo-bar",
    |         ^

See this issue (old but still applies). tl;dr rollup doesn't parse json imports out of the box and you need rollup-plugin-json for it

[chrisdothtml]

Closing in favor of #32