vimrc: Switched key for background toggle, repaired bg check

.vimrc

@@ -52,12 +52,12 @@ augroup XML
     autocmd FileType xml :%foldopen!
 augroup END
 
-if "$VIM_COLORSCHEME" == "light"
+if $VIM_COLORSCHEME == "light"
     set background=light
 endif
 set termguicolors
 colorscheme solarized
-call togglebg#map("<Leader>b")
+call togglebg#map("<Leader>t")
 let load_doxygen_syntax = 1
 let g:airline_powerline_fonts = 1
   if !exists('g:airline_symbols')