Fixes minor 7.1 incompatibilities
Add php7.1, remove hhvm (#13) HHVM build errors about ``` The command "sudo apt-get install -y hhvm" failed and exited with 100 during . ``` https://travis-ci.org/hostnet/symfony1/jobs/231082063
Add php7.1, remove hhvm (#13) HHVM build errors about ``` The command "sudo apt-get install -y hhvm" failed and exited with 100 during . ``` https://travis-ci.org/hostnet/symfony1/jobs/231082063