patch 9.0.1684: Update libvterm to rev 839

Problem: libvterm slightly outdated
Solution: Update libvterm from rev 818 to rev 839

Notable fix: libvterm now handles DECSM/DECRM with multiple arguents,
so several ncurses programs (e.g. nnn) can enable mouse properly when
run in Vim's terminal in XTerm.

closes: #12746

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
diff --git a/src/version.c b/src/version.c
index 34f1203..96c1817 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1684,
+/**/
     1683,
 /**/
     1682,