Node 10 EOL

[hugosenari]

Describe the bug

Node 10 are reaching EOL, AWS will deprecate it

Expected behavior Acceptance Tests and Circleci shouldn't run Node 10 anymore

Additional context We could also look for code improvements with new ES features available at Node 12. Ie:

• Array.prototype.values;
• Array.prototype.flat
• Array.prototype.flatMap
• Object.fromEntries
• Private class fields

TODO:

• [ ] Update serverless.yml
• [ ] Update package.json
• [ ] Update circleci/config.yml
• [ ] Update examples
• [ ] Update .nvmrc

see also #419 and #657