Update travis rbx configuration to be simpler

* Use the new rbx-19mode to setup testing under Rubinius' 1.9 mode instead of
  the more complex environment/exclusion scheme (that still needs to be used for
  jRuby since there is no jruby-18mode and jruby-19mode options yet)

.travis.yml

@@ -7,79 +7,58 @@ rvm:
   - ruby-head
   - ree
   - jruby
-  - rbx
+  - rbx-18mode
+  - rbx-19mode
 env:
   -
   - JRUBY_OPTS="--1.8"
   - JRUBY_OPTS="--1.9"
-  - RBXOPT="-X18"
-  - RBXOPT="-X19"
 matrix:
   exclude:
     # exclude 1.8.7
     - rvm: 1.8.7
       env: JRUBY_OPTS="--1.8"
     - rvm: 1.8.7
       env: JRUBY_OPTS="--1.9"
-    - rvm: 1.8.7
-      env: RBXOPT="-X18"
-    - rvm: 1.8.7
-      env: RBXOPT="-X19"
 
     # exclude 1.9.2
     - rvm: 1.9.2
       env: JRUBY_OPTS="--1.8"
     - rvm: 1.9.2
       env: JRUBY_OPTS="--1.9"
-    - rvm: 1.9.2
-      env: RBXOPT="-X18"
-    - rvm: 1.9.2
-      env: RBXOPT="-X19"
 
     # exclude 1.9.3
     - rvm: 1.9.3
       env: JRUBY_OPTS="--1.8"
     - rvm: 1.9.3
       env: JRUBY_OPTS="--1.9"
-    - rvm: 1.9.3
-      env: RBXOPT="-X18"
-    - rvm: 1.9.3
-      env: RBXOPT="-X19"
 
     # exclude ruby-head
     - rvm: ruby-head
       env: JRUBY_OPTS="--1.8"
     - rvm: ruby-head
       env: JRUBY_OPTS="--1.9"
-    - rvm: ruby-head
-      env: RBXOPT="-X18"
-    - rvm: ruby-head
-      env: RBXOPT="-X19"
 
     # exclude ree
     - rvm: ree
       env: JRUBY_OPTS="--1.8"
     - rvm: ree
       env: JRUBY_OPTS="--1.9"
-    - rvm: ree
-      env: RBXOPT="-X18"
-    - rvm: ree
-      env: RBXOPT="-X19"
 
     # exclude jruby
     - rvm: jruby
       env:
-    - rvm: jruby
-      env: RBXOPT="-X18"
-    - rvm: jruby
-      env: RBXOPT="-X19"
 
-    # exclude rbx
-    - rvm: rbx
-      env:
-    - rvm: rbx
+    # exclude rbx-18mode
+    - rvm: rbx-18mode
+      env: JRUBY_OPTS="--1.8"
+    - rvm: rbx-18mode
+      env: JRUBY_OPTS="--1.9"
+
+    # exclude rbx-19mode
+    - rvm: rbx-19mode
       env: JRUBY_OPTS="--1.8"
-    - rvm: rbx
+    - rvm: rbx-19mode
       env: JRUBY_OPTS="--1.9"
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