chore(colors): Set highlight links for NvimTreeStatusLine

[sindrets]

This sets some default highlight links for the new NvimTreeStatusLine highlight groups so that vim doesn't fill the statusline with carrots.

Example with minimal rc:

Before:

After:

fixes #332

[bandithijo]

Nice catch!

This is the standard behaviour of Vim.
If StatusLine and StatusLineNC have the same highlighting, the program will use the caret character (^) in the status line of the current window (in order to highlight it).

:help hl-StatusLineNC
---------------------

Note: if this is equal to "StatusLine" Vim will use "^^^" in the status line
of the current window.

Before this fix PR,

:verbose hi NvimTreeStatusLine
NvimTreeStatusLine xxx cleared

:verbose hi NvimTreeStatusLineNC
NvimTreeStatusLineNC xxx cleared

Both of them have cleared which are same.

I have manually solved with,

hi link NvimTreeStatusLine   StatusLine
hi link NvimTreeStatuslineNC StatusLineNC

But your solution is better.
Thank you 😄