Allow 403 errors on CI builds

Allowing 403 errors to pass CI lets us know that the API is still active but it doesn't like robots pinging its endpoint without a key.

.travis.yml

 language: ruby
 rvm: 2.2
 before_script: gem install awesome_bot
-script: awesome_bot README.md --allow-ssl
+script: awesome_bot README.md --allow-ssl --allow 403