fix build issue

Author: fholzer

.travis.yml

@@ -1,8 +1,15 @@
 language: generic
 
+dist: trusty
+sudo: required
+
 services:
   - docker
 
+before_install:
+  - echo '{"ipv6":true,"fixed-cidr-v6":"2001:db8:1::/64"}' | sudo tee /etc/docker/daemon.json
+  - sudo service docker restart
+
 install:
   - docker build -t nginx-brotli .