.gitignore: Ignore tarballs (*.gz)

This patch updates the root .gitignore file to ignore files with a .gz
extension. This will cause git to ignore downloaded sound tarballs in
the the sounds/ directory.

Change-Id: I1e42fbfa02a8884231507b683e8e49ac3e278aaa

.gitignore

@@ -9,6 +9,7 @@
 
 *~
 *.[oadi]
+*.gz
 *.ii
 *.oo
 *.eo