circleci: remove go-previous and export GO111MODULE=on

Author: umarcor

.circleci/config.yml

@@ -8,6 +8,7 @@ references:
     run:
       name: "All Commands"
       command: |
+        export GO111MODULE=on
         mkdir -p bin
         curl -Lso bin/shellcheck https://github.com/caarlos0/shellcheck-docker/releases/download/v0.4.6/shellcheck
         chmod +x bin/shellcheck
@@ -29,13 +30,6 @@ jobs:
       - run:
           name: "Check formatting"
           command: diff -u <(echo -n) <(gofmt -d -s .)
-  go-previous:
-    docker:
-      - image: circleci/golang:1.11
-    working_directory: *workspace
-    steps:
-      - checkout
-      - *run_tests
   go-latest:
     docker:
       - image: circleci/golang:latest
@@ -49,5 +43,4 @@ workflows:
   main:
     jobs:
       - go-current
-      - go-previous
       - go-latest