Update cw3-flex-multisig/helpers.ts to work with cosmjs/cli v0.26 and base-helpers.ts

[findolor]

In the examples, updated code works until we instantiate the contract.

Based on the contract schema if we give initMsg as

const initMsg = {
  group_addr: addr,
  threshold: {
    absolute_count: {
      weight: 5
    }
  },
  max_voting_period: {
    time: 3600
  }
}

it'll throw error saying Error parsing into type u64: EOF while parsing a JSON value.: instantiate wasm contract failed

Can't seem to get around this issue, would love to get some help on this!

Edit: Used cw4-group contract addr as the group_addr in initMsg to make it work.
https://github.com/CosmWasm/cw-plus/tree/main/contracts/cw3-flex-multisig#instantiation