Fix Travis build failures caused by sigh changes (#2859)
Fix Travis build failures caused by sigh changes (#2859)

* Test PR: debugging Travis build failures

* Don't use set -e

* Explicitly check for the existence of build/sigh.js

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