Require sudo for travis builds

This is a workaround to a problem with running Chrome Headless in `no-sandbox` mode, as discussed in this issue: travis-ci/travis-ci#8836 (comment)

Author: kimroen

.travis.yml

@@ -5,7 +5,7 @@ node_js:
   # so that your addon works for all apps
   - "4"
 
-sudo: false
+sudo: required
 dist: trusty
 
 addons: