Update iqsharp-base version to get security patches (#793)

Dockerfile

@@ -1,7 +1,7 @@
 # We use the iqsharp-base image, as that includes
 # the .NET Core SDK, IQ#, and Jupyter Notebook already
 # installed for us.
-FROM mcr.microsoft.com/quantum/iqsharp-base:0.24.210930
+FROM mcr.microsoft.com/quantum/iqsharp-base:0.24.216270-beta
 
 # Add metadata indicating that this image is used for the katas.
 ENV IQSHARP_HOSTING_ENV=KATAS_DOCKERFILE