Added missing source maps for Backbone 1.1.2 and Underscore 1.6.0.

The compressed files of Backbone v1.1.2 and Underscore v1.6.0 wanted to load the source maps for each of the files. These are not included in the repo so when loading tailon in the browser you get 404 when the browser tries to load the source maps.

I don't know if removing the `sourceMappingURL` declaration from each file is the preferred fix for this issue rather than adding the source maps. I can make a pull request for that instead if wanted.

I just want to avoid getting 404's when loading tailon in the browser :)