Upgrade `twiddle` to `2.0.0-alpha.7`.
Upgrade `twiddle` to `2.0.0-alpha.7`.

Twiddle was updated to perpetuate the new iterator type property of its
decorated iterator.

https://github.com/bigeasy/twiddle/releases/tag/v2.0.0-alpha.7

Closes #191.

bigeasy/splice,bigeasy/splice