Give travis-ci a break

ruby 1.9.2 will be EOL next month (June 2014)
and Rails 2.3 is EOL since a while now.

Currently a single commit trigger (4 * 5) - 2 = 38 travis builds
With this change 3 * 4 = 12 builds
Merge pull request #1226 from Shopify/give-travis-a-break

Give travis-ci a break