Fixing incorrect use of "it's" in docs.

Came across several of these when checking out the docs.

Here's the most succinct explanation that turned up quickly for "it's vs its" usage: http://www.diffen.com/difference/It's_vs_Its
>It's is a contraction for "it is". Its is like "his", "hers" or "theirs" and can be loosely translated as "belonging to it". When trying to decide which to use, just remember this: it's is the same as "it is". Only use it's when you are trying to abbreviate it is. In all other cases, use its (without the apostrophe).