[OTHER]update "typechain-target-truffle" to "@typechain/truffle-v5"

[osaguild]

What would you like to share?

Hi. it's my first contribution.

I think we need to update "typechain-target-truffle" to "@typechain/truffle-v5". Because this package has been deprecated.
https://www.npmjs.com/package/typechain-target-truffle

I trying to update it, but test doesn't pass. The reason is truffle migrated from "bignumber.js" to "BN.js" in v5, I need to change test code.
dethcrypto/TypeChain#211

How about this package update? If you need to update the package, I would like to assign this issue to me.

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