THRIFT-4990 Switch to .NET core 3.0
Client: netstsd
Patch: Jens Geyer

This closes #1909
diff --git a/build/docker/ubuntu-disco/Dockerfile b/build/docker/ubuntu-disco/Dockerfile
index b017c4e..b63fd58 100644
--- a/build/docker/ubuntu-disco/Dockerfile
+++ b/build/docker/ubuntu-disco/Dockerfile
@@ -130,7 +130,7 @@
 
 RUN apt-get install -y --no-install-recommends \
 `# dotnet core dependencies` \
-      dotnet-sdk-2.2
+      dotnet-sdk-3.0
 
 RUN apt-get install -y --no-install-recommends \
 `# Erlang dependencies` \