url: fix ancient syntax

[rbot] / .travis.yml

---
language: ruby
dist: bionic
before_install:
  - sudo apt-get update -y
  - sudo apt-get install -y libtokyocabinet-dev zlib1g-dev libbz2-dev libxml2-dev libxslt1-dev
script:
  - bundle exec rake test
rvm:
  - 2.7.0
  - 2.6.0
  - 2.5.0