patch 8.0.0867: job and channel in a dict value not quoted

Problem:    When using a job or channel value as a dict value, when turning it
            into a string the quotes are missing.
Solution:   Add quotes to the job and channel values. (Yasuhiro Matsumoto,
            closes #1930)
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index 98bc758..8c14fa4 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -18,6 +18,9 @@
   let g:job = term_getjob(buf)
   call assert_equal(v:t_job, type(g:job))
 
+  let string = string({'job': term_getjob(buf)})
+  call assert_match("{'job': 'process \\d\\+ run'}", string)
+
   return buf
 endfunc