Whitelist swagger.io due to bug

There's a known issue in awesome_bot; whitelisting swagger.io to
silence the warning pending upstream fix.

.travis.yml

@@ -1,4 +1,4 @@
 language: ruby
 rvm: 2.2
 before_script: gem install awesome_bot
-script: awesome_bot README.md --allow-redirect --allow-dupe --allow 429 -w .amazonaws.com,news.ycombinator.com 
+script: awesome_bot README.md --allow-redirect --allow-dupe --allow 429 -w .amazonaws.com,news.ycombinator.com,swagger.io