update circleci image.

Author: shirou

.circleci/config.yml

@@ -6,18 +6,12 @@ jobs:
   build:
     docker:
       # specify the version
-      - image: circleci/golang:1.15.6-buster
-
-      # Specify service dependencies here if necessary
-      # CircleCI maintains a library of pre-built images
-      # documented at https://circleci.com/docs/2.0/circleci-images/
-      # - image: circleci/postgres:9.4
+      - image: cimg/go:1.18.1
 
     #### TEMPLATE_NOTE: go expects specific checkout path representing url
     #### expecting it in the form of
     ####   /go/src/github.com/circleci/go-tool
     ####   /go/src/bitbucket.org/circleci/go-tool
-    working_directory: /go/src/github.com/{{ORG_NAME}}/{{REPO_NAME}}
     steps:
       - checkout