I think this would generate a string like `https:///travis-ci.org/travis-ci/travis-ci` (note the three `/`s). Note that `File.join` is platform-specific, so say if we for some reason started running travis-api on Windows machines, this would use `\` instead of `/`.

What do you think about just doing `webUrl="https://<%= Travis.config.client_domain %>/<%= r.slug %>"`?