patch 8.1.1502: cannot play any sound

Problem:    Cannot play any sound.
Solution:   Use libcanberra if available.  Add sound functions.
diff --git a/.travis.yml b/.travis.yml
index 51d3578..53331e6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -77,6 +77,7 @@
       - clang
       - lcov
       - gettext
+      - libcanberra-dev
       - libperl-dev
       - python-dev
       - python3-dev