travis: don't send email notifications

I never received any email from travis and actually don't want to. Thus, I'm
removing my email address from the notification list.

Signed-off-by: David Wagner <david.wagner@intel.com>
diff --git a/.travis.yml b/.travis.yml
index b50a84b..96a10bc 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -63,7 +63,5 @@
           --gcov-options '\--long-file-names --preserve-paths'
 
 notifications:
-  email:
-    - david.wagner@intel.com
   irc:
     - "chat.freenode.net#parameter-framework"