Disable 1.9.3 builds until upgraded from -preview1 to -rc1

Author: jeremy

.travis.yml

@@ -2,7 +2,7 @@ script: 'ci/travis.rb'
 rvm:
   - 1.8.7
   - 1.9.2
-  - 1.9.3
+  #- 1.9.3 # Disable 1.9.3 builds until Travis is on 1.9.3-rc1.
 env:
   - "GEM=railties"
   - "GEM=ap,am,amo,ares,as"