Cleanup .travis.yml so it can be updated more cleanly.

Use shared values in YAML so that only certain pieces of .travis.yml need to be updated in order to update Ruby versions.  Things should cascade so that if people send a pull request they can update just RVM field.

.travis.yml

@@ -8,15 +8,18 @@ rvm:
   - &ruby1 2.3.0
   - &ruby2 2.2.4
   - &ruby3 2.1.8
+  - &jruby 9.1.2.0
 
 matrix:
   include:
-    - rvm: 2.3.0
+    - rvm: *ruby1
       env: TEST_SUITE=fmt
-    - rvm: jruby-9.0.5.0
-      env: TEST_SUITE=test
-    - rvm: 2.3.0
-      env: TEST_SUITE=default-site
+    - env: TEST_SUITE=default-site
+      rvm: *ruby1
+  exclude:
+    - rvm *jruby
+      env: TEST_SUITE=cucumber
+    
 env:
   matrix:
     - TEST_SUITE=test