Upgrade Commoner and Populist to force upgrade to graceful-fs v2.0.0.

A silent upgrade from graceful-fs v1.2.2 to v1.2.3 (a dependency for both
Commoner and Populist) broke the build process, even though tests were
still passing. The 2.0.0 version fixes whatever was broken, though I won't
pretend to know exactly what the root cause was.
Merge pull request #195 from benjamn/force-upgrade-graceful-fs

Upgrade Commoner and Populist to force upgrade to graceful-fs v2.0.0