build+multi: switch from bolt to bbolt

In this commit, we switch from boltbd/bolt to coreos/bbolt as the
former is no longer being actively maintained.

discovery/gossiper.go

@@ -9,7 +9,7 @@ import (
 	"sync/atomic"
 	"time"
 
-	"github.com/boltdb/bolt"
+	"github.com/coreos/bbolt"
 	"github.com/davecgh/go-spew/spew"
 	"github.com/go-errors/errors"
 	"github.com/lightningnetwork/lnd/chainntnfs"