Add smokescreen test for Node support to travis.

[mramato]

This PR should fail, showing that Cesium is broken in Node (which it is). Once travis fails, I'll push a fix for Cesium in Node.

[cesium-concierge]

@mramato, thanks for the pull request! Maintainers, we have a signed CLA from @mramato, so you can review this at any time.

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[mramato]

The first build failed and I pushed a fix.

The real fix here is to make buildModuleUrl work in Node, but that is a little more involved and should be done as part of a separate PR. The important thing here is that we'll no longer accidentally ship a completely broken version of Cesium to Node users.

[mramato]

Not sure why this isn't showing up, but the build already passed: https://travis-ci.org/AnalyticalGraphicsInc/cesium/builds/336272112

This is good to go. We'll probably want to unpublish 1.42 from NPM as well