Merge remote-tracking branch 'bantu/ticket/12320' into develop-olympus

* bantu/ticket/12320:
  [ticket/12320] Install a nightly build of HHVM.
  [ticket/12320] No longer allow Travis CI HHVM environment to fail.

.travis.yml

@@ -33,5 +33,3 @@ matrix:
       env: DB=mariadb
     - php: 5.4
       env: DB=postgres
-  allow_failures:
-    - php: hhvm

travis/setup-webserver.sh

@@ -26,7 +26,7 @@ APP_SOCK=$(realpath "$DIR")/php-app.sock
 if [ "$TRAVIS_PHP_VERSION" = 'hhvm' ]
 then
 	# Upgrade to a recent stable version of HHVM
-	sudo apt-get -o Dpkg::Options::="--force-confnew" install -y hhvm
+	sudo apt-get -o Dpkg::Options::="--force-confnew" install -y hhvm-nightly
 
 	# MySQLi is broken in HHVM 3.0.0~precise and still does not work for us in
 	# 2014.03.28~saucy, i.e. needs more work. Use MySQL extension for now.