build(go mod): add go mod

Makefile

@@ -9,5 +9,5 @@ build:
 	promu build
 
 test:
-	go test -v -race
+	go test ./... -v -race
 	gocoverutil -coverprofile=coverage.txt test -v

go.mod

@@ -0,0 +1,26 @@
+module github.com/Percona-Lab/clickhouse_exporter
+
+go 1.13
+
+require (
+	github.com/AlekSi/gocoverutil v0.2.0 // indirect
+	github.com/Sirupsen/logrus v1.0.1
+	github.com/alecthomas/units v0.0.0-20190924025748-f65c72e2690d // indirect
+	github.com/beorn7/perks v1.0.1
+	github.com/golang/protobuf v1.3.4
+	github.com/google/go-github/v25 v25.1.3 // indirect
+	github.com/matttproud/golang_protobuf_extensions v1.0.1
+	github.com/pkg/errors v0.9.1 // indirect
+	github.com/prometheus/client_golang v1.4.1
+	github.com/prometheus/client_model v0.2.0
+	github.com/prometheus/common v0.9.1
+	github.com/prometheus/log v0.0.0-20151026012452-9a3136781e1f
+	github.com/prometheus/procfs v0.0.10
+	github.com/prometheus/promu v0.5.0 // indirect
+	golang.org/x/net v0.0.0-20200226121028-0de0cce0169b // indirect
+	golang.org/x/oauth2 v0.0.0-20200107190931-bf48bf16ab8d // indirect
+	golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae
+	golang.org/x/tools v0.0.0-20200227222343-706bc42d1f0d // indirect
+	google.golang.org/appengine v1.6.5 // indirect
+	gopkg.in/yaml.v2 v2.2.8 // indirect
+)