.functions: Make `np` remove `node_modules`

This lets you catch cases where you forgot to add a dependency to `package.json`.

Closes #321.
.osx: Support multiple `systemuiserver` pref files

Closes #319.
Merge branch 'master' of https://github.com/mathiasbynens/dotfiles

# By Manpreet Singh (1) and Sindre Sorhus (1)
# Via Mathias Bynens
* 'master' of https://github.com/mathiasbynens/dotfiles:
  .osx: Support multiple `systemuiserver` pref files
  .functions: Make `np` remove `node_modules`