vim: always use dark background

The reason for this is that in some servers the automatic detection (see
:help background) is guessing it wrong and using a light background,
consequently burning my eyeballs every time I open vim.

Hard coding the dark background seems fine for now, as I seem to never
really have a need for the light version. If the needs arises in the
future, then I'll have to come up with a better solution, but KISS for
now.

nvim/init.vim

@@ -4,6 +4,7 @@ if $XDG_DATA_HOME == "" | let $XDG_DATA_HOME="~/.local/share" | endif
 
 " Options {{{
 set   backspace=indent,eol,start  " sane backspace behavior
+set   background=dark   " always use dark background
 set nobackup            " don't keep backup file after overwriting a file
 set   clipboard=unnamedplus " synchronize with system clipboard
 set   colorcolumn=+1    " highlight column after 'textwidth'