Fix golangci-lint issues (attempt)

Related to: golangci/golangci-lint#827

Author: romanodesouza

.travis.yml

@@ -8,7 +8,7 @@ go:
 git:
   depth: 1
 install:
-  - GO111MODULE=off go get -u github.com/golangci/golangci-lint/cmd/golangci-lint
+  - go get github.com/golangci/golangci-lint/cmd/golangci-lint@v1.23.8
 script:
   - golangci-lint run
   - MEMCACHED_HOST="localhost:11211" REDIS_HOST="localhost:6379" go test -tags integration -v -race -coverprofile=coverage.txt -covermode=atomic ./...