vendor: update bbolt to v1.3.5

We had once updated bbolt from v1.3.3 to v1.3.4 in #4134,
but reverted to v1.3.3 in #4156 due to "fatal error: sweep increased
allocation count" (etcd-io/bbolt#214).

The issue was fixed in bbolt v1.3.5 (etcd-io/bbolt#220).

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/go.etcd.io/bbolt/cursor.go

@@ -366,7 +366,7 @@ func (c *Cursor) node() *node {
 	}
 	for _, ref := range c.stack[:len(c.stack)-1] {
 		_assert(!n.isLeaf, "expected branch node")
-		n = n.childAt(int(ref.index))
+		n = n.childAt(ref.index)
 	}
 	_assert(n.isLeaf, "expected leaf node")
 	return n