patch 8.0.0309: cannot use an empty key in json

Problem:    Cannot use an empty key in json.
Solution:   Allow for using an empty key.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    309,
 /**/
     308,
 /**/