Exclude unrelated directories from distribution

This should've been done before cutting the first release; the `./test/`
directory was accidentally bundled with v0.1.0, adding 4.4 MBs of unused
fixtures to the download.

package.json

@@ -3,6 +3,7 @@
  "version": "v0.1.0",
  "license": "ISC",
  "main": "./lib/index",
+ "files": ["bin", "lib"],
  "repository": "https://github.com/Alhadis/Roff.js",
  "description": "Troff integration with web technologies. Tools and postprocessors to generate web-based formats in Roff.",
  "keywords": ["troff", "groff", "nroff", "roff", "manpages", "ditroff", "postprocessing", "typesetting", "Electron", "Electroff"],