Removed syntastic and replaced it with ale

Read more here:
https://github.com/w0rp/ale

sources_non_forked/ale/ale_linters/elixir/credo.vim

@@ -0,0 +1,37 @@
+" Author: hauleth - https://github.com/hauleth
+
+function! ale_linters#elixir#credo#Handle(buffer, lines) abort
+    " Matches patterns line the following:
+    "
+    " lib/filename.ex:19:7: F: Pipe chain should start with a raw value.
+    let l:pattern = '\v:(\d+):?(\d+)?: (.): (.+)$'
+    let l:output = []
+
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        let l:type = l:match[3]
+        let l:text = l:match[4]
+
+        if l:type is# 'C'
+            let l:type = 'E'
+        elseif l:type is# 'R'
+            let l:type = 'W'
+        endif
+
+        call add(l:output, {
+        \   'bufnr': a:buffer,
+        \   'lnum': l:match[1] + 0,
+        \   'col': l:match[2] + 0,
+        \   'type': l:type,
+        \   'text': l:text,
+        \})
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('elixir', {
+\   'name': 'credo',
+\   'executable': 'mix',
+\   'command': 'mix help credo && mix credo suggest --format=flycheck --read-from-stdin %s',
+\   'callback': 'ale_linters#elixir#credo#Handle',
+\})