correct the travis exclusions for lower version of rails on 2.2

Author: JonRowe

.travis.yml

@@ -17,14 +17,15 @@ env:
   - RAILS_VERSION=4-1-stable
   - RAILS_VERSION=4-0-stable
   - RAILS_VERSION=3-2-stable
-  - RAILS_VERSION=3.2.16
   - RAILS_VERSION=3.1.12
   - RAILS_VERSION=3.0.20
 matrix:
   exclude:
     # MRI 2.2 is not supported on a few versions
     - rvm: 2.2
-      env: RAILS_VERSION='~> 3.1.12'
+      env: RAILS_VERSION=3.1.12
+    - rvm: 2.2
+      env: RAILS_VERSION=3.0.20
     # 3.0.x is not supported on MRI 2.0.0
     - rvm: 2.0.0
       env: RAILS_VERSION=3.0.20