neomake rules for mix test

neomake-mix-test.vim

let g:neomake_elixir_mix_maker = {
            \ 'args': ['compile'],
            \ 'errorformat':
            \ '** %s %f:%l: %m,' .
            \ '%f:%l: warning: %m'
            \ }
let g:neomake_elixir_test_maker = {
            \ 'exe': 'mix',
            \ 'args': ['test'],
            \ 'errorformat':
                \ '%Z       %f:%l,' .
                \ '%C     ** %m,' .
                \ '%C     %[%^:]%#:%.%#,' .
                \ '%C     %m,' .
                \ '%E  %n)%.%#'
            \ }