doc: make spelling of behavior consistent

In the api docs there were some instances of behaviour
and many more with behavior.  I was asked as part of a review
on a different PR which one to use and went with behavior
to be consistent with the majority.

Our style guide states that American English spelling is preferred.

PR-URL: https://github.com/nodejs/node/pull/13245


Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Kunal Pathak <kunal.pathak@microsoft.com>