patch 8.1.1691: diff test fails on some systems

Problem:    Diff test fails on some systems. (Elimar Riesebieter)
Solution:   Add a term_wait() call.
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index bf49740..f82a11c 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -743,6 +743,7 @@
   call term_sendkeys(a:buf, ":diffupdate!\<CR>")
   " trailing : for leaving the cursor on the command line
   call term_sendkeys(a:buf, ":set diffopt=internal,filler" . a:extra . "\<CR>:")
+  call term_wait(a:buf)
   call VerifyScreenDump(a:buf, a:dumpfile, {})
 endfunc
 
diff --git a/src/version.c b/src/version.c
index 0c56f7d..cc6dc44 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1691,
+/**/
     1690,
 /**/
     1689,