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.

autopilot/graph.go

@@ -7,7 +7,7 @@ import (
 	"sync/atomic"
 	"time"
 
-	"github.com/boltdb/bolt"
+	"github.com/coreos/bbolt"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/roasbeef/btcd/btcec"