Fix npm issues (node 0.10.x, npm 1.2.20)

Running `hoodie new myapp` throws two npm warnings:

    npm WARN package.json hoodie-app@0.5.0 No repository field.
    npm WARN engine hoodie-app@0.5.0: wanted: {"node":"0.8.x"} (current: {"node":"v0.10.7","npm":"1.2.21"})

The repository field was introduced in [npm 1.2.20](https://github.com/isaacs/npm/issues/3446), and setting the engine >= 0.8.x allows it to run also on newer node versions.