add ur toString

drongo

@@ -1 +1 @@
-Subproject commit c7e16a29e33d802ac209c046eddb5e040b76f704
+Subproject commit 6b4b2529c803581b13e1604acd230dff24c839b4

src/main/java/com/sparrowwallet/sparrow/ur/UR.java

@@ -81,6 +81,10 @@ public class UR {
         }
     }
 
+    public String toString() {
+        return UREncoder.encode(this);
+    }
+
     @Override
     public boolean equals(Object o) {
         if(this == o) {