a Travis build for node-webkit 0.10.0-RC1 (based on Node.js v0.11.13)

A newer node-webkit's version (v0.10.0-rc1) is based on Node.js v0.11.13; a support for the latter was introduced by #184.

This pull request adds a Travis CI build for that node-webkit's version.

It made necessary to (additionally) preinstall a couple of i386 packages (because of Chromium differences introduced in this new node-webkit's version, I presume).

Several changes in node-pre-gyp were necessary as well. (The corresponding pull requests are mapbox/node-pre-gyp#92 and mapbox/node-pre-gyp#93.)