ADD rubocop linter

ale_linters/ruby/rubocop.vim

@@ -0,0 +1,46 @@
+if exists('g:loaded_ale_linters_ruby_rubocop')
+    finish
+endif
+
+let g:loaded_ale_linters_ruby_rubocop = 1
+
+function! ale_linters#ruby#rubocop#Handle(buffer, lines)
+    " Matches patterns line the following:
+    "
+    " <text>:47:14: Missing trailing comma. [Warning/comma-dangle]
+    " <text>:56:41: Missing semicolon. [Error/semi]
+    " let pattern = '.*_:\(\d\+\):\(\d\+\): \(.\) \(.\+\)'
+    let pattern = '\v_:(\d+):(\d+): (.): (.+)'
+    let output = []
+
+    for line in a:lines
+        let l:match = matchlist(line, pattern)
+
+        if len(l:match) == 0
+            continue
+        endif
+
+        let text = l:match[4]
+        let type = l:match[3]
+
+        " vcol is Needed to indicate that the column is a character.
+        call add(output, {
+        \   'bufnr': a:buffer,
+        \   'lnum': l:match[1] + 0,
+        \   'vcol': 0,
+        \   'col': l:match[2] + 0,
+        \   'text': text,
+        \   'type': type ==# 'C' ? 'E' : 'W',
+        \   'nr': -1,
+        \})
+    endfor
+
+    return output
+endfunction
+
+call ALEAddLinter('ruby', {
+\   'executable': 'rubocop',
+\   'command': 'rubocop --format emacs --stdin _',
+\   'callback': 'ale_linters#ruby#rubocop#Handle',
+\})
+