Update CI matrix more

Excluding some invalid combinations.

Author: enkessler

.travis.yml

@@ -19,7 +19,11 @@ matrix:
     # Ruby 2.3.x is currently broken on TravisCI for OSX and is no longer a supported Ruby version, anyway.
   - rvm: 2.3
     os: osx
-
+    # CukeModeler 3.x requires at least Ruby 2.3
+  - rvm: 2.0
+    gemfile: testing/gemfiles/cuke_modeler3.gemfile
+  - rvm: 2.2
+    gemfile: testing/gemfiles/cuke_modeler3.gemfile
 
 gemfile:
   - testing/gemfiles/cuke_modeler1.gemfile