Update Buffer initialization to non-deprecated method

[cwardcode]

Description

The purpose of this pull request is to update the Buffer initializations within the utility.js file away from the deprecated method (calling the Buffer constructor) , and instead call Buffer.from().

Calling the Buffer constructor has been deprecated and results in the following message during runtime, as detailed here:

The Buffer() and new Buffer() constructors are not recommended for use due to security and usability concerns. Please use the new Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() construction methods instead.

References

Issue #150

Testing

No tests have been added, although the test suite was re-ran and all tests are still passing.

Checklist

• [no] I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• [yes] All active GitHub checks for tests, formatting, and security are passing
• [n/a (using master)] The correct base branch is being used, if not master

[ottokruse]

Yes! I'm so tired of finding these in my logs

[DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.

[jimmyjames]

Thanks for the contribution @cwardcode! 👍

[ottokruse]

When are you guys gonna publish to npm?