attempt to enable ipv6 on travis

.travis.yml

@@ -3,6 +3,10 @@ language: go
 go:
     - "1.14.x"
 
+before_install:
+  # https://github.com/travis-ci/travis-ci/issues/8361
+  - sudo sh -c 'echo 0 > /proc/sys/net/ipv6/conf/all/disable_ipv6'
+
 script:
 - make
 - make test