Update circleci/golang Docker tag to v1.13.0 (#89)

renovate[bot] · Yusuke Kato · commit 3b2d2cf6a6d1 · 2019-09-14T11:20:50.000+09:00
diff --git a/.circleci/config.yml b/.circleci/config.yml
@@ -2,7 +2,7 @@ alias:
   default: &default
     working_directory: /go/src/github.com/kpango/gache
     docker:
-      - image: circleci/golang:1.12.9
+      - image: circleci/golang:1.13.0
         environment:
           GOPATH: "/go"
           GO111MODULE: "on"
