travis: Disable email notifications

I'm getting spammed.  We'll see the results in the status.

Closes: #450
Approved by: jlebon

.travis.yml

@@ -11,3 +11,6 @@ env:
 script:
   - tests/ci-install.sh
   - ci_parallel=2 ci_sudo=yes tests/ci-build.sh
+
+notifications:
+  email: false