Behat Symfony2Extension has symfony/symfony: ~2.1 as a dev requirement. On Travis, it requires it with a more strict requirement (to test against different versions).
This was working properly 24 days ago (for the previous Travis build) but it is failing today with a weird output: it installed 2.3.1 and then tried to find 2.2.*.
See https://travis-ci.org/Behat/Symfony2Extension/jobs/8623568 for the output.
The latest composer is used as it runs self-update at the beginning of the build.
Closing as it's very old.