Fix arm32 Docker

Dockerfile.arm

@@ -6,6 +6,7 @@ WORKDIR /repo
 COPY . .
 #TODO Remove or update the sed line when we update dotnet version.
 RUN export DOTNET_CLI_TELEMETRY_OPTOUT=1 \
+ && find . -type f -exec sed -i 's/netcoreapp2.1/netcoreapp3.0/g' {} \; \
  && dotnet clean -maxcpucount:1 \
  && dotnet publish \
     -maxcpucount:1 \