Fix syntax error in exists function (#297)

Fix syntax error in `exists` function

In GH-296 a syntax errors has crept in where the `exists` function was
missing the second `s` in two cases.

Fixes GH-299
GH-297


Co-authored-by: Julien Voisin <jvoisin@users.noreply.github.com>
Co-authored-by: Sven Greb <development@svengreb.de>
Co-authored-by: Arctic Ice Studio <development@arcticicestudio.com>

colors/nord.vim

@@ -726,7 +726,7 @@ endif
 "+--- Languages ---+
 " Haskell
 " > neovimhaskell/haskell-vim
-if exist('g:cabal_indent_section')
+if exists('g:cabal_indent_section')
   call s:hi("haskellPreProc", s:nord10_gui, "", s:nord10_term, "", "", "")
   call s:hi("haskellType", s:nord7_gui, "", s:nord7_term, "", "", "")
   hi! link haskellPragma haskellPreProc
@@ -859,7 +859,7 @@ hi! link mkdDelimiter Keyword
 
 " PHP
 " > StanAngeloff/php.vim
-if exist('g:php_version_id')
+if exists('g:php_version_id')
   call s:hi("phpClass", s:nord7_gui, "", s:nord7_term, "", "", "")
   call s:hi("phpClassImplements", s:nord7_gui, "", s:nord7_term, "", s:bold, "")
   hi! link phpClassExtends phpClass