added package.json for jspm

This makes the bootstrap dependency explicit, as well as ensuring it is served minified with a source map generated when loaded from github:ajkochanowicz/tinygrowl.

I've also added it to the jspm registry here - https://github.com/jspm/registry/blob/master/registry.json#L17.

This means users only need to do: `jspm.import('tinygrowl@1.0');` to get everything (including bootstrap) loaded.

I would suggest tagging this as a new `1.0.1` release. Let me know if that all makes sense!