fix golint issues in core/stores (#527)

core/stores/postgres/postgresql.go

@@ -8,6 +8,7 @@ import (
 
 const postgresDriverName = "postgres"
 
+// New returns a postgres connection.
 func New(datasource string, opts ...sqlx.SqlOption) sqlx.SqlConn {
 	return sqlx.NewSqlConn(postgresDriverName, datasource, opts...)
 }