Segfault when using Node 0.12

[mike-north]

Due to a known libsass issue, users of ember-cli-sass will currently get segfaults when using node.js 0.12

The fix for this is to NOT use node-sass ~3.5.0. While acknowledging that the root cause of the problem does not lie with this library, I suggest changing the constraint in your package.json to ~3.4.2 or something, to prevent users from having a bad experience.

[simonexmachina]

The solution to this issue is to specify which version of node-sass to use until the underlying issue is fixed.