Update to node16

[llunaCreixent]

• Update node in .nvmrc
• npm install with node 16
• Add node engine in package.json
• Update dependencies: @babel/core, @truffle/contract, @truffle/hdwallet-provider, chai, eslint, eslint-plugin-import, web3
• Remove dependencies (detected with depcheck): @truffle/error, ethers
• Special cases:
  • @openzeppelin/contracts updated to last version using solc-0.7 (https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v4.0.0)
  • ganache and truffle updates make tests fail

Closes https://github.com/CirclesUBI/circles-contracts/issues/185

[llunaCreixent]

tests pass with node16 branch of dockers (https://github.com/CirclesUBI/circles-docker/pull/84)