adding netcore2 back in per eric until he can clean some stuff up

Dockerfile

@@ -108,12 +108,23 @@ set mouse= \n\
 imap jj <Esc> \n\
 ' >> /etc/vim/vimrc
 
-
-# region NETCORE3
+# region NETCORE
 # taken from https://hub.docker.com/_/microsoft-dotnet-core-sdk
 # taken from https://github.com/dotnet/dotnet-docker/blob/master/3.0/sdk/bionic/amd64/Dockerfile
 
-# Install .NET Core SDK
+# Install .NET Core 2 SDK
+ENV DOTNET_SDK_VERSION 2.1.500
+ENV DOTNET_SDK_DOWNLOAD_URL https://dotnetcli.blob.core.windows.net/dotnet/Sdk/$DOTNET_SDK_VERSION/dotnet-sdk-$DOTNET_SDK_VERSION-linux-x64.tar.gz
+ENV DOTNET_SDK_DOWNLOAD_SHA 85055728e2433dfde41d15c85475f2dc6cfdd30242b4b23065b63cb12cc846acb93c09c000b02b722890ceac8ac382b40871c78660716ca2339c71052fe52f4e
+ENV NUGET_XMLDOC_MODE skip
+RUN curl -SL $DOTNET_SDK_DOWNLOAD_URL --output dotnet.tar.gz \
+    && echo "$DOTNET_SDK_DOWNLOAD_SHA dotnet.tar.gz" | sha512sum -c - \
+    && mkdir -p /usr/share/dotnet \
+    && tar -zxf dotnet.tar.gz -C /usr/share/dotnet \
+    && rm dotnet.tar.gz \
+    && ln -s /usr/share/dotnet/dotnet /usr/bin/dotnet
+
+# Install .NET Core 3 SDK
 ENV DOTNET_SDK_VERSION 3.0.100
 
 RUN curl -SL --output dotnet.tar.gz https://dotnetcli.blob.core.windows.net/dotnet/Sdk/$DOTNET_SDK_VERSION/dotnet-sdk-$DOTNET_SDK_VERSION-linux-x64.tar.gz \