Updated Isabelle base image.

2021-03-21 00:00:13 +00:00 · 2021-03-21 00:00:13 +00:00 · b96397800d
--- a/.ci/isabelle4isadof/Dockerfile
+++ b/.ci/isabelle4isadof/Dockerfile
@ -24,7 +24,7 @@
 #
 # SPDX-License-Identifier: BSD-2-Clause

-FROM logicalhacking/lh-docker-isabelle:isabelle2020
+FROM logicalhacking/lh-docker-isabelle:isabelle2021

 WORKDIR /home/isabelle
 COPY thy_output.ML /home/isabelle/Isabelle/src/Pure/Thy