Build against node-webkit version 0.11.2

Recent improvements of our code base have made it possible to target the newest version of the unstable node-webkit's branch.

This pull request ensures that the next versions of sqlite3 are built against node-webkit version 0.11.2 on Mac, on Linux and on Windows.

The branch has passed its tests [on Travis CI](https://travis-ci.org/mapbox/node-sqlite3/builds/43685633) and also [on AppVeyor](https://ci.appveyor.com/project/Mapbox/node-sqlite3/build/1.0.228). I feel safe to merge it myself.