According to https://github.com/equalsraf/neovim-qt/issues/604, nvim-qt will set the termguicolors
options when it is started. However, if we add `set notermguicolors` in init.vim, the nvim-qt setting will
not take effect after nvim-qt is started. So we need to remove the `set notermguicolors` setting in the
config.
We can not detect whether nvim-qt is loaded when sourcing `init.vim`.
If termguicolors option is not set, we use a better color (badwolf in this case).
Gruvbox8 is terrible when termguicolors is not set.
