modified to use newer opam

codinuum · codinuum · commit 232477d74084 · 2021-10-15T08:59:57.000+09:00
diff --git a/Dockerfile b/Dockerfile
@@ -1,4 +1,4 @@
-FROM ubuntu:20.04
+FROM ubuntu:21.04
 
 MAINTAINER codinuum
 
