Update .travis.yml (#27)

* Update Travis config to use dpl v2 (https://docs.travis-ci.com/user/deployment-v2)

Author: calvellido

.travis.yml

@@ -53,7 +53,8 @@ jobs:
         - BUNDLE_GEMFILE=./docs/Gemfile bundle exec jekyll build -s docs -d gen-docs
       deploy:
         provider: pages
-        cleanup: true
+        edge: true
+        cleanup: false
         token: $GITHUB_TOKEN
         keep_history: true
         local_dir: gen-docs