graceful-fs@2 and @3 support will be removed soon

[ChALkeR]

Hi. zuul is currently #52 in my list of modules that would likely to be broken when nodejs/node#6413 lands (which is anticipated to happen before v7.0).

Note that graceful-fs@1 and graceful-fs@4 are ok and would not be broken by this, but a require() on graceful-fs@2 or graceful-fs@3 would cause an error soon.

That is, runtime warning fs: re-evaluating native module sources is not supported. would be turned into a throw.

If you or your deps use graceful-fs@2 or graceful-fs@3 in runtime — you are affected.

Tracking: nodejs/node#5213.

[defunctzombie]

We do not directly depend on graceful fs, which of our modules do we actually need to upgrade?