fix typo in api docs by changing `iff` to `if`

[shaunlebron]

Hi! These docstrings are parsed straight from the clojurescript repo. Having said that, iff is actually math-speak for if-and-only-if.

I've seen others confused by the obscurity of this abbreviation, so if you want, you can either submit patches to clojurescript to rename iff => if and only if in the official docstrings, or submit a Summary entry for our api docs to use instead:

• https://github.com/cljs/api/blob/master/docfiles/cljs.core/defonce.md
• https://github.com/cljs/api/blob/master/docfiles/cljs.spec/STAR.md

[DataDaoDe]

Hey Shaun, thanks for the info. I was wondering about that since the "iff" occurred twice which seemed odd. So I'll take a look at patching cljs and see if I can get that through since that would take care of the confusion everywhere.