patch 8.1.0720: cannot easily change the current quickfx list index

Problem:    Cannot easily change the current quickfx list index.
Solution:   Add the "idx" argument to setqflist(). (Yegappan Lakshmanan,
            closes #3701)
diff --git a/src/version.c b/src/version.c
index 6ec6033..60dadf1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -796,6 +796,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    720,
+/**/
     719,
 /**/
     718,