Update circleci to 2.1, add anchore image scanning config

[lewisdaly]

Part of #1003

• update circleci config
• add anchore image scanning
• bump package version to 8.6.1

[lewisdaly]

This is failing due to upgrades to joi-currency-code:3.0.0, which doesn't return a proper Joi Object, but instead a dict which we can no longer call Joi.extend() on.

[lewisdaly]

Closed in favour of #291