Add license to bower.json

[chulkilee]

I would be great to pull from the original package's package.json, but I don't know how files in this directory is generated.

[chrisirhc]

They're from https://github.com/angular-ui/bootstrap

[chulkilee]

What I wanted to know was build system/script, not the source. Seems like these files are manually pushed.

Created PR #31, so closing it.