Update index.d.ts

[finntenzor]

Support customize sequelize for typescript.

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Only affected your code tips if you use typescript.

Description of change

Add the Sequelize options declare. It was supported long time ago but not mentioned in the index.d.ts.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@683298d). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #80   +/-   ##
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  Coverage          ?   84.37%           
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  Files             ?        4           
  Lines             ?       64           
  Branches          ?        0           
=========================================
  Hits              ?       54           
  Misses            ?       10           
  Partials          ?        0

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