Luacheck: Respect warn_about_trailing_whitespace option

See http://luacheck.readthedocs.io/en/stable/warnings.html, warnings
611 to 614.

ale_linters/lua/luacheck.vim

@@ -26,6 +26,12 @@ function! ale_linters#lua#luacheck#Handle(buffer, lines) abort
     let l:output = []
 
     for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        if !ale#Var(a:buffer, 'warn_about_trailing_whitespace')
+        \   && l:match[3] is# 'W'
+        \   && index(range(611, 614), str2nr(l:match[4])) >= 0
+            continue
+        endif
+
         call add(l:output, {
         \   'lnum': l:match[1] + 0,
         \   'col': l:match[2] + 0,