Load grunt-sed via HTTPS

Created by: ncksllvn

Since all other dependencies are loaded via HTTPS, it makes sense to load grunt-sedthe same way even though it's being pulled from GitHub. I had some problems installing it while behind a firewall but had no problems installing any of the others.

"grunt-sed": "git+https://github.com/twbs/grunt-sed.git#v0.2.0",