Fix go imports in distlock.go after etcd changed urls

The etcd project has switched from github.com URLs to
go.etcd.io URLs. The import statements in distlock.go
have been updated to reflect this. The old imports
failed to compile. See here for details:
etcd-io/etcd#10044 (comment)

distlock.go

@@ -4,9 +4,9 @@ import (
 	"context"
 	"flag"
 	"fmt"
-	v3 "github.com/coreos/etcd/clientv3"
-	"github.com/coreos/etcd/clientv3/concurrency"
-	"github.com/coreos/etcd/mvcc/mvccpb"
+	v3 "go.etcd.io/etcd/clientv3"
+	"go.etcd.io/etcd/clientv3/concurrency"
+	"go.etcd.io/etcd/mvcc/mvccpb"
 	"gopkg.in/yaml.v2"
 	"io/ioutil"
 	"log"