According to the discussion in https://github.com/ezsystems/developer-documentation/pull/1012#discussion_r403894334 we should upgrade our Docker setup to use Node 12 for v3, but keep Node 10 for running tests with version 2.

Node 10 is installed here: https://github.com/ezsystems/docker-php/blob/master/php/Dockerfile-node#L6
Maybe we should prepare a new format-version, so that ezsystems/php:7.3-v1-node uses Node10 and ezsystems/php:7.3-v2-node uses Node 12?

Scope of this task:

• add the possibility to use Node12 in our Docker stack (while keeping the option to use Node10)
• change tests running on 3.0 and master to use Node12