Escher has been repurposed to be a metapackage around Interact.jl and other packages for web deployment (so far it includes Mux.jl but more things may be added as they become available). Refer to the Interact documentation (in particular the deployment section).
You can replace
using Interact, Mux with
using Escher, i.e.:
using Escher ui = @manipulate for i in 1:100 i end webio_serve(page("/", req -> ui))