travis-ci: Work around broken /etc/hosts on trusty env

.travis.yml

@@ -3,7 +3,11 @@ dist: trusty
 language: c
 
 before_install:
+  # Trusty related fixed
+  # multiverse is no on trusty activated (https://github.com/travis-ci/travis-ci/issues/4979)
   - sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu/ trusty multiverse" && sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu/ trusty-updates multiverse"
+  # /etc/hosts has IPv6 hosts (https://github.com/travis-ci/travis-ci/issues/4978)
+  - sudo [ $(ip addr show | grep "inet6 ::1" | wc -l) -lt "1" ] && sudo sed -i '/^::1/d' /etc/hosts
   - sudo apt-get update -qq
   - sudo apt-get purge -qq gawk
   # http://docs.travis-ci.com/user/trusty-ci-environment/ indicates, no MySQL on Trusty (yet)