Updated Docker Ubuntu base image to newest hirsute.

Thanks to xet7 !

.devcontainer/Dockerfile

@@ -1,4 +1,4 @@
-FROM quay.io/wekan/ubuntu:groovy-20201125.2
+FROM quay.io/wekan/ubuntu:hirsute-20210522
 LABEL maintainer="sgr"
 
 # 2020-12-03:

Dockerfile

@@ -1,4 +1,4 @@
-FROM quay.io/wekan/ubuntu:groovy-20210115
+FROM quay.io/wekan/ubuntu:hirsute-20210522
 LABEL maintainer="wekan"
 
 # 2020-12-03: