Update dependencies

I needed mocha to be updated for the changes they made to using `this` within tests for https://github.com/marionettejs/backbone.marionette/pull/1373. I updated mocha to 1.19 and fs-extra to 0.9.1 since I was already updating stuff.

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**Changes:**
- Updated `mocha` and `fs-extra` npm dependencies to latest versions

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Let me know if you need anything else, thanks.