provider: ruby: Use stderr_buffered to collect stderr

runtime/autoload/provider/ruby.vim

@@ -4,16 +4,7 @@ if exists('g:loaded_ruby_provider')
 endif
 let g:loaded_ruby_provider = 1
 
-let s:stderr = {}
+let s:job_opts = {'rpc': v:true, 'stderr_buffered': v:true}
-let s:job_opts = {'rpc': v:true}
-
-function! s:job_opts.on_stderr(chan_id, data, event) abort
-  let stderr = get(s:stderr, a:chan_id, [''])
-  let last = remove(stderr, -1)
-  let a:data[0] = last.a:data[0]
-  call extend(stderr, a:data)
-  let s:stderr[a:chan_id] = stderr
-endfunction
 
 function! provider#ruby#Detect() abort
   if exists("g:ruby_host_prog")
@@ -36,14 +27,15 @@ function! provider#ruby#Require(host) abort
   endfor
 
   try
-    let channel_id = jobstart(prog, s:job_opts)
+    let job = copy(s:job_opts)
+    let channel_id = jobstart(prog, job)
     if rpcrequest(channel_id, 'poll') ==# 'ok'
       return channel_id
     endif
   catch
     echomsg v:throwpoint
     echomsg v:exception
-    for row in get(s:stderr, channel_id, [])
+    for row in get(job, 'stderr', [])
       echomsg row
     endfor
   endtry