Normally I would let `eslint --fix` do this for me, but there's a bug
that causes:
const x = function ()
{
// ...
};
to become:
const x = ()
=> {
// ...
};
which ESLint thinks is a syntax error. (It probably is; I don't know
enough about the automatic semicolon insertion rules to be confident.)
Clearing the authorship colors of a document with at least two authors, and then
undoing that action caused a disconnect from the pad.
This change disallows undoing clearing authorship colors in order to prevent
the problem from affecting users, and adds the relative test coverage.
This is a change of behaviour, and is documented in the changelog.
Fixes#2802 (sidestepping it).
