patch 8.1.1310: named function arguments are never optional

Problem:    Named function arguments are never optional.
Solution:   Support optional function arguments with a default value. (Andy
            Massimino, closes #3952)
diff --git a/src/version.c b/src/version.c
index b8acb8f..57aff32 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1310,
+/**/
     1309,
 /**/
     1308,