package.json: bump version 0.2.12 -> 0.2.13

New features:
- LibreWolf is now supported (0cbb89b)

Fixes:
- Blurry fonts on HiDPI (83c066f)
- Breakage caused by incorrect parsing of msgpack encodings introduced
  in recent Neovim versions (b959588)
- Breakage caused by Neovim's removal of $NVIM_LISTEN_ADDRESS (8e6eaa8)
- Not working on some nix installations (458ccfe)
- Breakage when Neovim emits messages on startup (1f91597)
- Breakage caused by XDG env variables missing (f17b672)