Change "check-box" to "checkbox" in the docs.

Review Request #5539 — Created Feb. 24, 2014 and submitted — Latest diff uploaded

Information

Review Board
release-2.0.x
c48e452...

Reviewers

The existing docs were using "check-box," which is wrong. I guess I
added this ages ago, but I'm not sure why.

This replaces all occurrences with "checkbox."

Built the docs and saw the changes.

Grepped through all the docs for all occurrences.