Fix Travis config to support PHP v5.3

[terales]

We have an error at Travis job:

PHP 5.3 is supported only on Precise.
See https://docs.travis-ci.com/user/reference/trusty#PHP-images on how to test PHP 5.3 on Precise.

Solution is to add php 5.3 to matrix:

matrix:
  include:
    - php: 5.3
      dist: precise