Fix the package to use `blaze` for `Handlebars` for Meteor 1.0.

In meteor 1.0, `Handlebars` is exposed by blaze package, rather than the empty handlebars package.

ref
https://github.com/meteor/meteor/blob/devel/packages/blaze/backcompat.js
https://github.com/meteor/meteor/tree/devel/packages/handlebars