[ruby-cvs:79087] f132825ffa (master): Disable IPv6 on Travis s390x case. (#2819)

Jun Aruga	2020-01-07 12:23:04 +0900 (Tue, 07 Jan 2020)

  New Revision: f132825ffa

  https://github.com/ruby/ruby/commit/f132825ffa

  Log:
    Disable IPv6 on Travis s390x case. (#2819)
    =

    This fixes following error that sometimes happens once in a few times=
=0D
    on Travis s390x environment.=0D
    =0D
    ```=0D
    $ tool/travis_retry.sh sudo -E apt-add-repository -y "ppa:ubuntu-tool=
chain-r/test"=0D
    + sudo -E apt-add-repository -y ppa:ubuntu-toolchain-r/test=0D
    Error: retrieving gpg key timed out.=0D
    ```

  Added files:
    tool/travis_disable_ipv6.sh
  Modified files:
    .travis.yml=