v0.2.1

Security update.

• Updated axios, avoiding CVE-2021-3749. The potential impact of this security vulnerability should have been fairly low: when using
  the axios backend (but not the fetch backend), a malicious API server could have provoked long processing times, by sending response headers with long sequences of interior whitespace. This would likely have required custom server software, since common servers like Apache and nginx limit the maximum header length, and the performance impact appears to be negligible at 8K characters.
• Updated other dependencies.