fix(colors): adjust SpellBad highlighting (#52)

Define `SpellBad` highlighting rule to improve readability.

Closes #47

Signed-off-by: Orlando Hohmeier <hello@orlandohohmeier.com>

Author: Orlando Hohmeier

colors/dracula.vim

@@ -67,6 +67,7 @@ hi SpecialKey ctermfg=231 ctermbg=235 cterm=NONE guifg=#525563 guibg=NONE gui=NO
 hi Statement ctermfg=212 ctermbg=NONE cterm=NONE guifg=#ff79c6 guibg=NONE gui=NONE
 hi StorageClass ctermfg=117 ctermbg=NONE cterm=NONE guifg=#8be9fd guibg=NONE gui=italic
 hi String ctermfg=228 ctermbg=NONE cterm=NONE guifg=#f1fa8c guibg=NONE gui=NONE
+hi SpellBad ctermfg=red ctermbg=NONE cterm=underline
 hi Tag ctermfg=212 ctermbg=NONE cterm=NONE guifg=#ff79c6 guibg=NONE gui=NONE
 hi Title ctermfg=231 ctermbg=NONE cterm=bold guifg=#f8f8f2 guibg=NONE gui=bold
 hi Todo ctermfg=61 ctermbg=NONE cterm=inverse,bold guifg=#6272a4 guibg=NONE gui=inverse,bold