React to SDK renaming to linux-musl-x64

Backport dd1934771fab67f8e2c3e965a821f8b94f472008

build/docker/alpine.Dockerfile

@@ -33,6 +33,6 @@ ENV KOREBUILD_SKIP_RUNTIME_INSTALL=1
 COPY global.json /tmp/global.json
 RUN DOTNET_SDK_VERSION="$(jq -r '.sdk.version' /tmp/global.json)" \
     && echo "Installing SDK ${DOTNET_SDK_VERSION}" \
-    && wget -q --tries 10 -O /tmp/dotnet.tar.gz https://dotnetcli.blob.core.windows.net/dotnet/Sdk/$DOTNET_SDK_VERSION/dotnet-sdk-$DOTNET_SDK_VERSION-alpine.3.6-x64.tar.gz \
+    && wget -q --tries 10 -O /tmp/dotnet.tar.gz https://dotnetcli.blob.core.windows.net/dotnet/Sdk/$DOTNET_SDK_VERSION/dotnet-sdk-$DOTNET_SDK_VERSION-linux-musl-x64.tar.gz \
     && mkdir -p "$HOME/.dotnet" \
     && tar xzf /tmp/dotnet.tar.gz -C "$HOME/.dotnet"