Cannot convert a BigInt value to a number
Hello,

It seems there is a bug, we are using `Math.max` for BigInt numbers, which is not supported.

When using `wallet.getNumBlocksToUnlock()` I get the following error:

```
TypeError: Cannot convert a BigInt value to a number
    at Math.max (<anonymous>)
    at MoneroWalletFull.getNumBlocksToUnlock (/home/sina/Projects/pouch-js/node_modules/monero-ts/src/main/ts/wallet/MoneroWallet.ts:448:38)
    at <anonymous> (/home/sina/Projects/pouch-js/test.ts:21:19)
```