Include -cover for test coverage

Signed-off-by: Alex Ellis <[email protected]>

Dockerfile

@@ -9,7 +9,7 @@ RUN test -z "$(gofmt -l $(find . -type f -name '*.go' -not -path "./vendor/*"))"
 RUN VERSION=$(git describe --all --exact-match `git rev-parse HEAD` | grep tags | sed 's/tags\///') \
  && GIT_COMMIT=$(git rev-list -1 HEAD) \
  && CGO_ENABLED=0 GOOS=linux go build --ldflags "-s -w -X github.com/openfaas/faas-cli/commands.GitCommit=${GIT_COMMIT} -X github.com/openfaas/faas-cli/commands.Version=${VERSION}" -a -installsuffix cgo -o faas-cli .
-RUN go test ./...
+RUN go test ./... -cover
 
 FROM alpine:latest
 RUN apk --no-cache add ca-certificates