patch 8.1.1508: sound keeps failing on Travis

Problem:    Sound keeps failing on Travis.
Solution:   Throw a skipped exception in the test.
diff --git a/src/version.c b/src/version.c
index 6b6fd19..1156fd6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1508,
+/**/
     1507,
 /**/
     1506,