Improve guard so it works for no eof new line

compiler/mix.vim

@@ -1,4 +1,5 @@
 if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'elixir') == -1
+
 if exists('current_compiler')
     finish
 endif
@@ -15,4 +16,5 @@ CompilerSet errorformat=
             \%E==\ Compilation\ error\ in\ file\ %f\ ==,
             \%C**\ (%\\w%\\+)\ %f:%l:\ %m,%Z
 
+
 endif