THRIFT-4990 Upgrade to .NET Core 3.1 (LTS)
Client: netstd
Patch: Jens Geyer

This closes #1961
diff --git a/build/docker/ubuntu-bionic/Dockerfile b/build/docker/ubuntu-bionic/Dockerfile
index d38901f..79d698f 100644
--- a/build/docker/ubuntu-bionic/Dockerfile
+++ b/build/docker/ubuntu-bionic/Dockerfile
@@ -130,7 +130,7 @@
 
 RUN apt-get install -y --no-install-recommends \
 `# dotnet core dependencies` \
-      dotnet-sdk-3.0
+      dotnet-sdk-3.1
 
 RUN apt-get install -y --no-install-recommends \
 `# Erlang dependencies` \