Bump ruby 2.6 -> 2.7 to fix packagecloud deploy step

See StackStorm/st2#6068

Author: arm4b

.circleci/config.yml

@@ -150,7 +150,7 @@ jobs:
             - el8
   deploy:
     docker:
-      - image: ruby:2.6.3
+      - image: ruby:2.7
     environment:
       ARTIFACTS: /home/circleci/artifacts
       DISTROS: bionic focal el7 el8