add mac-specific rb-fsevent gem for guard

Added rb-fsevent gem for mac-specific platforms. This is in response to receiving 'inotify not found' errors on a mac. 
Oh crap, sorry about that! I’ll be more careful in the future. 


On Oct 8, 2014, at 4:25 PM, Robert Fletcher <notifications@github.com> wrote:

> In Gemfile.lock:
> 
> > @@ -124,7 +125,7 @@ GEM
> >      reportable (1.1.2)
> >        activerecord (>= 2.0.0)
> >        activesupport (>= 2.0.0)
> > -    rmagick (2.13.1)
> > +    rmagick (2.13.3)
> You also bumped up the rmagick version here. I'll go ahead and merge since I think it should be fine, but double check for unintended additions when you commit.
> 
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