patch 8.1.1644: sound test does not work on Travis

Problem:    Sound test does not work on Travis.
Solution:   Use "sg" command to enable audio. (Ozaki Kiichi, closes #4624)
diff --git a/src/version.c b/src/version.c
index c7e2a16..754155b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1644,
+/**/
     1643,
 /**/
     1642,