Update node version to 16 to fix CI

[Luni-4]

Checklist:

• All tests pass in CI.
• There are sufficient tests for the new fix/feature.
• Grammar rules have not been renamed unless absolutely necessary.
• The conflicts section hasn't grown too much.
• The parser size hasn't grown too much (check the value of STATE_COUNT in src/parser.c).

This PR updates the node version in order to fix CI tests. @aryx we should land this one before other PRs in this way we know if all tests pass.

Thanks in advance for your review! :)

[aryx]

thx!