Try re-enabling HHVM (last part of #176)

.travis.yml

@@ -7,6 +7,7 @@ dist: trusty
 php:
   - 7.0
   - 7.1
+  - hhvm
   - nightly
 
 matrix:
@@ -16,7 +17,7 @@ matrix:
 before_script:
   - curl -sSL https://dl.bintray.com/xp-runners/generic/xp-run-master.sh > xp-run
   - echo "test.xar" > composer.pth
-  - if [ -f /etc/hhvm/php.ini ] ; then (echo "hhvm.php7.all = 1"; echo "hhvm.hack.lang.look_for_typechecker = 0") | sudo tee -a /etc/hhvm/php.ini ; fi
+  - if [ -f /etc/hhvm/php.ini ] ; then (echo "hhvm.php7.all = 1"; echo "hhvm.hack.lang.look_for_typechecker = 0") | sudo tee -a /etc/hhvm/php.ini ; hhvm --version ; fi
 
 script:
   - (EXCD=0; for i in `ls -1 src/test/config/unittest/*.ini`; do echo "---> $i"; sh xp-run xp.unittest.Runner $i; RES=$?; if [ $RES -ne 0 ]; then EXCD=$RES; fi; done; exit $EXCD;)