Catch fs.watch exceptions

[campersau]

• Files / directories might get deleted between is.directory / is.file / fs.readdir and the actual fs.watch call.
• electron monkey patches the fs API to transparently support files contained in asar archives but fs.watch does not work for them. (See https://github.com/FredrikNoren/ungit/issues/1523)

To test this I relied on the fact the the options are getting copied with Object.assign({}, options, {...}) so that I could delete the directory before fs.watch is called but after the is.directory / is.file checks.

Fixes https://github.com/yuanchuan/node-watch/issues/108

[yuanchuan]

Thank you