Minor errors exclamation marks in README

They must be from an earlier version/API or typos, but some examples ns/function names had missing exclamations.

update: heck, they are both there, how did I miss that. I had the exclamation-less failing on me but I should have checked the source. I was already wondering why supervise didn't seem to diff with or without.

I assume the exclamation(less) versions are for with/without side-effects? Anyway, I guess you can delete this, I can't.