Change library scrypt.js to scryptsy

[jimni1222]

Proposed changes

Many people are experiencing errors when building because of scrypt.
Removed the dependency on scrypt.js and replaced it with scryptsy.

This change reflects the content of web3.js v1.2.1. Here are some links:
refer web3/web3.js#3051
refer web3/web3.js#2913
refer https://github.com/ethereum/web3.js/pull/2937/files

https://github.com/ethereum/web3.js/blob/v1.2.1/packages/web3-eth-accounts/src/scrypt.js

Types of changes

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• Bugfix
• New feature or enhancement
• Others

Checklist

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• I have read the CONTRIBUTING GUIDELINES doc
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• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Related issues

close #91

Further comments

I'm concerned about the impact of this PR and ran all the tests described in package.json.
The tests didn't reveal any issues but if you're concerned about this change, please tell me.