Upgrade to contracts-upgradeable 3.3 + with EIP712

Support Upgrades
2

Hi @DarkPay,

I will have to come back to you if you can upgrade from OpenZeppelin Contracts Ethereum Package 3.0 to OpenZeppelin Contracts Upgradeable 3.3.

As OpenZeppelin Contracts Ethereum Package has an Initializable with a uint256[50] private ______gap;, whilst Initializable in OpenZeppelin Contracts Upgradeable is without a gap state variable.

Please note: We’ve decided it’s best to focus our upgradeability efforts on the Upgrades Plugins exclusively, and have halted development on the OpenZeppelin CLI. We will continue to provide support for the CLI until the end of 2020.
See: Building for interoperability: why we’re focusing on Upgrades Plugins

I suggest you look to migrate to Upgrades Plugins: https://docs.openzeppelin.com/upgrades-plugins/1.x/migrate-from-cli