build: update btcwallet to version with seed restore fix

Fixes #3223.

go.mod

@@ -8,7 +8,7 @@ require (
 	github.com/btcsuite/btcd v0.0.0-20190614013741-962a206e94e9
 	github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f
 	github.com/btcsuite/btcutil v0.0.0-20190425235716-9e5f4b9a998d
-	github.com/btcsuite/btcwallet v0.0.0-20190619005538-de02d6fdfb23
+	github.com/btcsuite/btcwallet v0.0.0-20190620233257-46c0cf2a3f3a
 	github.com/btcsuite/fastsha256 v0.0.0-20160815193821-637e65642941
 	github.com/coreos/bbolt v1.3.2
 	github.com/davecgh/go-spew v1.1.1