modify --watch option: continue when SyntaxError

i want 'mocha --watch' continue when SytaxError.
becase rerun is a little difficultiy. (running happy!)
but was stopped 'mocha --watch' when SytaxError.

this modify ...
 * when command start and SytaxError then stopped.
 * when 'mocha --watch' runninng and modify js SytaxError then running.