Upgrade to kibana-rack 0.1.3

My sincere apologies for the regression in 0.1.1. This new release serves the dashboard files from the correct path (`app/dashboards`, not `app/dashboard/{file,script}/dashboard.{js,json}) with the proper MIME types now.

[Compare for 0.1.1 -> 0.1.3](https://github.com/tabolario/kibana-rack/compare/v0.1.1...v0.1.3)