Update to latest ember-cli-sass to avoid deprecation warnings on node 6

[mdentremont]

• Indirectly, the latest version of upstream ember-cli-sass has newer version of node-sass which avoids a deprecation warning

[mike-north]

We were using an older version to support 0.12. Will this new version work too?

[mdentremont]

Given the readme comment:

1.11.0 <= x < 1.13.0 == v0.18.6

I thought 1.12 wasn't supported on the latest versions of ember-cli-materialize?

[mike-north]

Sorry, I should have been more clear. Node.js 0.12 is still an active LTS release, and we are obligated to support it. We've seen issues with newer versions of ember-cli-sass causing segfaults and other problems in node 0.12 (i.e. #319)

[mdentremont]

@mike-north Ah I see.

I believe the segfault you fixed in the fork was being introduced by an older version of broccoli-sass. Newer versions of https://github.com/aexmachina/ember-cli-sass do not use broccoli-sass anymore - so hopefully don't have that issue.

Also worth noting is that the tests & build run successfully on Node 0.12.

[mike-north]

Merged in #401 . Now ember-cli 2.6.0 is a minimum requirement for easy installation due to not using the patched ember-cli-sass