Update go version to 1.13.4

Author: Amey Bhide

.circleci/config.yml

@@ -10,7 +10,7 @@ jobs:
   build:
     working_directory: /go/workdir/src/github.com/splunk/vault-plugin-splunk
     docker:
-      - image: circleci/golang:1.12
+      - image: circleci/golang:1.13.4
         <<: *defaultenv
       - image: splunk/splunk:latest
         user: root

Makefile

@@ -36,7 +36,7 @@ lint: dep
 
 .PHONY: dep
 dep:
-	./scripts/golangci-lint.sh -b $(GOBIN) v1.17.1
+	./scripts/golangci-lint.sh -b $(GOBIN) v1.20.0
 
 .PHONY: clean
 clean: