Set the `minimum-stability` to `dev` for the master branch as it requires dev versions of `phpunit/php-timer`, `sebastian/diff`, and `sebastian/exporter`.
Simplified the travis config file a bit.
Merge pull request #821 from whatthejeff/composer-minimum-stability
Merge pull request #822 from whatthejeff/simplify-travis
Also test with PHP 5.5
Revert "Also test with PHP 5.5"

This reverts commit 1af126c4066e340f0c4e3e66d276d85dda24ea7e.