patch 8.1.1619: tests are not run with GUI on Travis

Problem:    Tests are not run with GUI on Travis.
Solution:   Add a testgui job. (Ozaki Kiichi, closes #4609)
diff --git a/src/version.c b/src/version.c
index 10e4c40..e86b5bf 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1619,
+/**/
     1618,
 /**/
     1617,