Support : sequelize v6 & sequelize typescript v2

[Yash-g17]

Added support for sequelize version 6 and sequelize-typescrirpt v2 Also upgraded typescript version.

Fix: https://github.com/node-casbin/sequelize-adapter/issues/34

[coveralls]

Pull Request Test Coverage Report for Build 715993266

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 86.232%

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Totals
Change from base Build 425597281:	0.0%
Covered Lines:	94
Relevant Lines:	102

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💛 - Coveralls

[hsluoyz]

@Yash-g17 hi, sorry that I have to revert this PR. Because we use Yarn instead of NPM. Can you re-send a PR with modifying yarn.lock ?

[Yash-g17]

Okay , on it .