Update Docker containers to dotnet 3.0

Dockerfile

@@ -1,4 +1,4 @@
-ARG DOTNET_VERSION=2.2
+ARG DOTNET_VERSION=3.0
 ARG FFMPEG_VERSION=latest
 
 FROM node:alpine as web-builder

Dockerfile.arm

@@ -17,8 +17,6 @@ FROM mcr.microsoft.com/dotnet/core/sdk:${DOTNET_VERSION} as builder
 WORKDIR /repo
 COPY . .
 ENV DOTNET_CLI_TELEMETRY_OPTOUT=1
-# TODO Remove or update the sed line when we update dotnet version.
-RUN find . -type f -exec sed -i 's/netcoreapp2.1/netcoreapp3.0/g' {} \;
 # Discard objs - may cause failures if exists
 RUN find . -type d -name obj | xargs -r rm -r
 # Build

Dockerfile.arm64

@@ -17,8 +17,6 @@ FROM mcr.microsoft.com/dotnet/core/sdk:${DOTNET_VERSION} as builder
 WORKDIR /repo
 COPY . .
 ENV DOTNET_CLI_TELEMETRY_OPTOUT=1
-# TODO Remove or update the sed line when we update dotnet version.
-RUN find . -type f -exec sed -i 's/netcoreapp2.1/netcoreapp3.0/g' {} \;
 # Discard objs - may cause failures if exists
 RUN find . -type d -name obj | xargs -r rm -r
 # Build