travis test matrix excludes rvm 1.9.3 when puppet < 3.0

http://docs.puppetlabs.com/guides/platforms.html#ruby-versions
asserts that Puppet older than 3.0 do not support Ruby 1.9.3

After this commit, the travis test matrix aligns with
the PuppetLabs platform support matrix as currently published.

.travis.yml

@@ -19,3 +19,5 @@ matrix:
     env: PUPPET_VERSION="~> 2.7.0"
   - rvm: 2.0.0
     env: PUPPET_VERSION="~> 3.1.0"
+  - rvm: 1.9.3
+    env: PUPPET_VERSION="~> 2.7.0"