Switch travis build to php 5.4 and 5.5.

[njam]

We're starting to use php 5.4 language features, so we should drop php 5.3 support, and make sure the travis build for 5.4 and 5.5 succeeds.

We still have those strange segmentation faults:

Time: 57.35 seconds, Memory: 66.00Mb
OK, but incomplete or skipped tests!
Tests: 757, Assertions: 4695, Skipped: 1.
/home/travis/build.sh: line 309: 20952 Segmentation fault      bin/phpunit
The command "bin/phpunit" exited with 139.

Ideas:

• Isolating and resolving the error source (Disable Kiss Tracking tests on Travis #1046)
• Expect this specific error, and "catch" it in bash

[njam]

done in #1183