bumping go version

.circleci/config.yml

@@ -3,7 +3,7 @@ jobs:
   build:
     working_directory: /go/src/github.com/wcharczuk/go-chart
     docker:
-      - image: circleci/golang:1.11
+      - image: circleci/golang:1.15
     steps:
       - checkout
       - run:
@@ -11,7 +11,4 @@ jobs:
           command: make new-install
       - run:
           name: ci
-          command: make ci
-      - store_artifacts:
-          path: coverage.html
-          destination: coverage.html
+          command: make ci