inherit transition from this._select instead of global one to work on…

[vegertar]

… shadow DOM

Description

fix #129

When work on shadow DOM the ordinarily global transition() will cause error: transition 1 not found which are generally due to a detached selection. To inherit transition parameters a proper way is defining a root transition on a root selection as explained by mbostock.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [ ] I have documented all new methods.
• [ ] I have written tests for all new methods/functionality.
• [ ] I have written examples for all new methods/functionality.

[davelandry]

Great work here @vegertar 👏🏻

My apologies for the delay in the review, got swamped at work. I'll be publishing a release with this fix in the next few minutes.