Also test in PHP7 mode

Author: fredemmott

.travis.sh

@@ -10,3 +10,6 @@ cd /var/source
 hhvm /usr/local/bin/composer install
 hh_server --check $(pwd)
 hhvm vendor/bin/phpunit tests/
+if [ $(hhvm --php -r 'echo HHVM_VERSION_ID;' 2>/dev/null) -ge 32002 ]; then
+  hhvm -d hhvm.php7.all=1 vendor/bin/phpunit tests/
+fi