Fix tests against php 7.4snapshot
Fix tests against php 7.4snapshot

* Install libonig-dev as it is temporarily required for snapshot and nighly tests (see https://github.com/travis-ci/php-src-builder/pull/36)

malarzm/mongodb-odm,malarzm/mongodb-odm,doctrine/mongodb-odm,alcaeus/mongodb-odm,alcaeus/mongodb-odm,doctrine/mongodb-odm