Add gruvbox light support

[jupblb]

Added support for gruvbox-light and gruvbox-white in relation to sharkdp/bat#1069 (released in 0.16.0)

[dandavison]

Thanks @jupblb! I've pushed one commit to your branch, pulling in the new binary assets from bat so that the gruvbox themes are included in delta. For the record, doing this is pretty simple:

In the bat repo:

1. git fetch --tags
2. git checkout v0.16.0
3. git submodule update

Then copy assets/*.bin from the bat repo to etc/assets/ in the delta repo.

[jupblb]

Thanks for stepping in and fixing this issue. I didn't notice that this was part of the codebase. ;)

[tgy]

Thanks! Can't wait for the next release with my favourite light colorscheme 👍