Update to latest s/fn-spec API
Update to latest s/fn-spec API

Fixes #315

mfikes/planck,slipset/planck,mfikes/planck,mfikes/planck,mfikes/planck,slipset/planck,slipset/planck,mfikes/planck,mfikes/planck,slipset/planck,slipset/planck