Fix all errors from golangci-lint command

Signed-off-by: Arjun Naik <arjun.rn@gmail.com>

.travis.yml

@@ -5,13 +5,15 @@ go:
   - "1.11.x"
 
 env:
-- GO111MODULE=on
+- GO111MODULE=on GOLANGCI_RELEASE="v1.16.0"
 
 before_install:
   - go get github.com/mattn/goveralls
   - go get github.com/lawrencewoodman/roveralls
+  - curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh -s -- -b $(go env GOPATH)/bin ${GOLANGCI_RELEASE}
 
 script:
+  - make check
   - make test
   - make build.docker
   - roveralls