Minor spelling correction to the leadership section of the handbook.

Made a minor spelling correction to the leadership section of the handbook. I wanted to try something small and inconsequential to learn how to use GitLab to make these kinds of changes. In this case, I just edited the file directly without creating a branch prior ... testing to see if this works. GL made me select a source branch and defaulted to patch-263. I'm not sure what that is, but gave it a shot.