.travis.yml in tracker_api-1.8.0 vs .travis.yml in tracker_api-1.9.0

@@ -3,9 +3,10 @@
 rvm:
   - 2.1
   - 2.2
   - 2.3
   - 2.4
+  - 2.5
   # - "jruby"
   #  - rbx
   #  - "1.8.7"
 # uncomment this line if your project needs to run something other than `rake`:
 # script: bundle exec rspec spec