fix golint issues (#1027)

core/stores/clickhouse/clickhouse.go

@@ -1,6 +1,7 @@
 package clickhouse
 
 import (
+	// imports the driver, don't remove this comment, golint requires.
 	_ "github.com/ClickHouse/clickhouse-go"
 	"github.com/tal-tech/go-zero/core/stores/sqlx"
 )

core/stores/postgres/postgresql.go

@@ -1,6 +1,7 @@
 package postgres
 
 import (
+	// imports the driver, don't remove this comment, golint requires.
 	_ "github.com/lib/pq"
 	"github.com/tal-tech/go-zero/core/stores/sqlx"
 )