What does this PR do?

Updates CircleCI config file:

• Update docker image
• change environment value from list to map

Additional context

Update docker image

The cimg/node docker image supercedes the legacy CircleCI Node.js image, circleci/node.

Early 2020, CircleCI released smaller, faster, more deterministic images. The node images can be found here. The intention of this commit is to optimise the build.

change environment value from list to map

Reference