Update node engine to v14

[mikesposito]

This package is still using Node.js v12, while our module template uses v16.

We should:

• Use v16 in our .nvmrc file
• Update engines section in package.json file with:

{
    "node": ">=14.0.0"
} 

• Update nodejs version used by circle-ci workflows

This is needed also to add @lavamoat/allow-scripts and update to yarn v3 (See #165)