Documentation: How to update the Travis Docker-image (#4108)
Documentation: How to update the Travis Docker-image (#4108)

* Created instructions for manually updating the docker image

* updated numbering

PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs,PolymerLabs/arcs