.travis.yml in backlog_kit-0.16.0 vs .travis.yml in backlog_kit-0.17.0

@@ -1,11 +1,13 @@
 language: ruby
 rvm:
   - 2.0.0
   - 2.1.10
-  - 2.2.8
-  - 2.3.5
-  - 2.4.2
+  - 2.2.10
+  - 2.3.7
+  - 2.4.4
+  - 2.5.1
+  - ruby-head
 before_install:
   - gem update --system
   - gem update bundler
 env:
   global: