Fix branch name in multi-repo client example (#651)

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>
diff --git a/examples/multirepo/client/client_example.go b/examples/multirepo/client/client_example.go
index 346f26c..87f1046 100644
--- a/examples/multirepo/client/client_example.go
+++ b/examples/multirepo/client/client_example.go
@@ -33,8 +33,8 @@
 )
 
 const (
-	metadataURL = "https://raw.githubusercontent.com/theupdateframework/go-tuf/main/examples/multirepo/repository/metadata"
-	targetsURL  = "https://raw.githubusercontent.com/theupdateframework/go-tuf/main/examples/multirepo/repository/targets"
+	metadataURL = "https://raw.githubusercontent.com/theupdateframework/go-tuf/master/examples/multirepo/repository/metadata"
+	targetsURL  = "https://raw.githubusercontent.com/theupdateframework/go-tuf/master/examples/multirepo/repository/targets"
 	verbosity   = 4
 )