Print post-processing error in multi-line paragraph

Related #510

plug.vim

@@ -1044,14 +1044,14 @@ function! s:update_finish()
         call s:log4(name, 'Updating submodules. This may take a while.')
         let out .= s:bang('git submodule update --init --recursive 2>&1', spec.dir)
       endif
-      let msg = printf('%s %s: %s', v:shell_error ? 'x': '-', name, s:lastline(out))
+      let msg = s:format_message(v:shell_error ? 'x': '-', name, out)
       if v:shell_error
         call add(s:update.errors, name)
         call s:regress_bar()
         silent execute pos 'd _'
         call append(4, msg) | 4
       elseif !empty(out)
-        call setline(pos, msg)
+        call setline(pos, msg[0])
       endif
       redraw
     endfor

test/workflow.vader

@@ -1397,8 +1397,9 @@ Execute (Commit hash support):
   call plug#end()
   PlugUpdate
   Log getline(1, '$')
-  AssertEqual 'x goyo.vim: error: pathspec ''ffffffff'' did not match any file(s) known to git.', getline(5)
-  AssertEqual 0, stridx(getline(6), '- vim-emoji: HEAD is now at 9db7fcf...')
+  AssertEqual 'x goyo.vim:', getline(5)
+  AssertEqual '    error: pathspec ''ffffffff'' did not match any file(s) known to git.', getline(6)
+  AssertEqual 0, stridx(getline(7), '- vim-emoji: HEAD is now at 9db7fcf...')
 
   let hash = system(printf('cd %s && git rev-parse HEAD', g:plugs['vim-emoji'].dir))[:-2]
   AssertEqual '9db7fcfee0d90dafdbcb7a32090c0a9085eb054a', hash