use node:16, not ubuntu+npm+node

Author: rpardini

Dockerfile

@@ -1,7 +1,5 @@
-FROM ubuntu:rolling as nodebuilder
+FROM node:16 as nodebuilder
 ENV DEBIAN_FRONTEND=noninteractive
-RUN apt-get -y update
-RUN apt-get -y install nodejs npm
 WORKDIR /js
 COPY fluidsignalr/ClientApp/package*.json /js/
 RUN npm ci
@@ -23,7 +21,7 @@ WORKDIR /app/fluidsignalr
 
 # Copy the js dist from the nodebuilder stage; the csproj has a target to copy it over to the out dir
 COPY --from=nodebuilder /js/dist /app/fluidsignalr/ClientApp/dist
-RUN dotnet publish -c Release -o out
+RUN dotnet publish -c Release  -o out 
 
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 ### Final runtime image