Currently quite some travis tests fail with:
Could not fetch https://api.github.com/repos/sebastianbergmann/phpunit-mock-objects/zipball/1.2.3, enter your GitHub credentials to go over the API rate limit
The credentials will be swapped for an OAuth token stored in /home/travis/.composer/config.json, your password will not be stored
To revoke access to this token you can visit https://github.com/settings/applications
No output has been received in the last 10 minutes, this potentially indicates a stalled build or something wrong with the build itself.
The build has been terminated
https://github.com/composer/composer/issues/1314 states some options to circumvent that.