change travis.yml to use multi versions of libclang

Current travis-ci configuration is to use libclang-3.3 only. This change enables to use multi versions of libclang from 3.2 to 3.5(snapshot) and with ruby-2.0 and ruby-2.1.

Some tests will fail on libclang 3.2 and 3.3 because newer APIs are used in this library. I will fix tests in near future for 3.2 and 3.3. Of course on 3.4 and 3.5, all tests succeed.