Mention ^string, ^number in "Type hinting" section

[vemv]

https://github.com/clojure/clojurescript-site/blob/0ef3da1d56fed6d9de322fed4973f2b17ecf6a9e/content/about/differences.adoc#hinting says:

the only type hint of significance is the ^boolean type hint: It is used to avoid checked if evaluation (which copes with the fact that, for example, 0 and "" are false in JavaScript and true in ClojureScript).

, but that's not true anymore given the ^string, ^number additions.