Docker hub is limiting pull rate

[elsid]

Thit leads to failing jobs with error:

ERROR: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit

Example job: https://travis-ci.org/github/yandex/ozo/jobs/773612976

Options to resolve:

1. Use custom docker registry.
2. Create https://hub.docker.com/ account and use docker login.
3. Do not use docker in CI (maybe switch to github actions).