Update highlight groups of Nvim-Tree icons

[antoineco]

As reported in

• Nvim-Tree git status icon highlight groups changes sonokai#127

highlight groups used for icons in Nvim-Tree were renamed in

• feat(#2415): highlight overhaul (#2454) nvim-tree/nvim-tree.lua#2455

The detailed changes are here: https://github.com/nvim-tree/nvim-tree.lua/blob/v1.14.0/doc/nvim-tree-lua.txt#L3102