feat(lambda): add a newVersion method

[skinny85]

This method is useful when deploying a Lambda through a CodePipeline.
It creates a new Version every time the CDK code is executed,
that way making sure an updated Lambda Alias will not point to an old Version.

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Pull Request Checklist

• Testing
  • Unit test added (prefer not to modify an existing test, otherwise, it's probably a breaking change)
  • CLI change?: coordinate update of integration tests with team
  • cdk-init template change?: coordinated update of integration tests with team
• Docs
  • jsdocs: All public APIs documented
  • README: README and/or documentation topic updated
• Title and Description
  • Change type: title prefixed with fix, feat will appear in changelog
  • Title: use lower-case and doesn't end with a period
  • Breaking?: last paragraph: "BREAKING CHANGE: <describe what changed + link for details>"
  • Issues: Indicate issues fixed via: "Fixes #xxx" or "Closes #xxx"
• Sensitive Modules (requires 2 PR approvers)
  • IAM Policy Document (in @aws-cdk/aws-iam)
  • EC2 Security Groups and ACLs (in @aws-cdk/aws-ec2)
  • Grant APIs (only if not based on official documentation with a reference)

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license.

[sam-goodwin]

What's up with the new-lines here?

[skinny85]

I generally try to break docs on sentence boundaries, so that future diffs of changes here will look better.

The newlines are not rendered in the docs themselves.

[Doug-AWS]

Is any of this visible to the user? Would they care?

[skinny85]

Is any of this visible to the user? Would they care?

Yes. Yes.

[skinny85]

Rebased and changed the method to use Date#toISOString().

[rix0rrr]

I kinda would hope we'd have a better solution than this (source hash, most likely), but until we do this'll do (pig).