Update CircleCI image to v4

.circleci/config.yml

@@ -2,7 +2,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: cppalliance/boost_superproject_build:20.04-v1
+      - image: cppalliance/boost_superproject_build:20.04-v4
     parallelism: 2
     steps:
       - checkout