travis.yml needs to be updated

[hjhsalo]

• Small updates

  • Update .travis.yml for Python 3.6
    • Just version string update (should bring 3.6.1)
  • Update ES to 2.4.6
    • Just version string update

• Bigger updates

  • Update to Bionic environment
    https://docs.travis-ci.com/user/reference/bionic/
  • Test
    • Check python version (should be 3.6.9)
    • Check redis version
    • Check rabbitmq version
  • Specify Redis and RabbitMQ version in .travis.yml
  • Test
  • Update PostgreSQL to newer than 9.6
    https://docs.travis-ci.com/user/database-setup/#using-a-different-postgresql-version
    NOTE: "For PostgreSQL 10 you must specify the packages to install it and the user is postgres and the port is 5432. For PostgreSQL 11 and 12 you must specify the packages, but the user is travis and the port is 5433 instead. So you must specify the PGPORT"
  • Test