.travis.yml in faraday_middleware-aws-signers-v4-0.1.5 vs .travis.yml in faraday_middleware-aws-signers-v4-0.1.6

@@ -1,10 +1,12 @@
 sudo: false
 cache: bundler
 language: ruby
 rvm:
   - 2.0.0
-  - 2.1.5
-  - 2.2.1
+  - 2.1.10
+  - 2.2.6
+  - 2.3.3
+  - 2.4.0
 script:
   - bundle install
   - bundle exec rake