Pin docker version to fix CI breakage from Go 1.15

Author: cbrewster

.circleci/config.yml

@@ -5,23 +5,26 @@ jobs:
       - image: docker:18.09
     steps:
       - checkout
-      - setup_remote_docker
+      - setup_remote_docker:
+          version: 18.09.3
       - run: apk add --no-cache --no-progress make git
       - run: make test
   build_and_test_changed:
     docker:
       - image: docker:18.09
     steps:
       - checkout
-      - setup_remote_docker
+      - setup_remote_docker:
+          version: 18.09.3
       - run: apk add --no-cache --no-progress make git
       - run: make changed-test
   build_test_and_deploy:
     docker:
       - image: docker:18.09
     steps:
       - checkout
-      - setup_remote_docker
+      - setup_remote_docker:
+          version: 18.09.3
       - run: apk add --no-cache --no-progress make git
       - run: make test
       - deploy: