patch 8.0.0310: not enough testing for GUI functionality

Problem:    Not enough testing for GUI functionality.
Solution:   Add tests for v:windowid and getwinpos[xy](). (Kazunobu Kuriyama)
diff --git a/src/version.c b/src/version.c
index dbe0dcb..187602c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    310,
+/**/
     309,
 /**/
     308,