Delete D. typo

[gaffney2010]

I think that the D. here is a typo, but logger without the prefix is a local variable and seems to work on my end.

This resulted in me getting the error message:

E5113: Error while calling lua chunk:
.../.local/share/nvim/plugged/gp.nvim/lua/gp/dispatcher.lua:43: attempt to index field 'logger' (a nil value) stack traceback:
.../.local/share/nvim/plugged/gp.nvim/lua/gp/dispatcher.lua:43: in function 'setup' ~/.local/share/nvim/plugged/gp.nvim/lua/gp/init.lua:73: in function 'setup'
~/.config/nvim/init.lua:133: in main chunk

After this fix, this outputs the expected message "Provider 1 is missing endpoint." This error message was probably not triggered in testing.