removing deprecated ruby version

Dave Try · Dave Try · commit b1380e10e7b0 · 2018-06-01T11:41:01.000+10:00
diff --git a/.travis.yml b/.travis.yml
@@ -4,7 +4,6 @@ bundler_args: --without development system_tests
 before_install: rm Gemfile.lock || true
 sudo: false
 rvm:
-  - 2.1.6
   - 2.2.5
   - 2.3.3
 script:
