fix: add a test to check for circle ring closure

[llamington]

Adds a test to satisfy https://github.com/d3/d3-geo/issues/289

[Fil]

Upgrading the test is not enough; we'll want to add a test for the case that breaks, and fix the generator: https://github.com/d3/d3-geo/blob/8c53a90ae70c94bace73ecb02f2c792c649c86ba/src/circle.js#L20

(this should probably store the starting point and repeat it at the end).