Proposal to remove travis test for php 5.2

As the before_script call now installs composer, this loses travis support for 5.2 already, and so travis tests have been failing since.
I think either we remove 5.2 from here like in this commit, or we remove the composer install, or if needed a hybrid approach where we have a bash script run as the before_script that checks the php version, and only for 5.3+ installs composer. Though i guess it depends on how important 5.2 support is to the project.

(also added php 5.5 to test on)