Use same version of Ruby X-API is: now 2.2.5.

.travis.yml

     packages:
       - tree
 before_install:
-  - rvm install 2.2.1
-  - rvm use 2.2.1
+  - rvm install 2.2.5
+  - rvm use 2.2.5
 
 script:
   - bin/run-unit-tests-in-ci.sh