[travis-ci] Workaround composer cache invalidation
[travis-ci] Workaround composer cache invalidation

see: https://github.com/travis-ci/travis-ci/issues/2435

akrabat/zend-validator,Maks3w/zend-validator,zf2timo/zend-validator,zendframework/zend-validator,ezimuel/zend-validator,svycka/zend-validator