Restore then() functionality

utils/GunSmith/GunSmith.js

@@ -400,6 +400,13 @@ function createReplica(path, afterMap = false) {
           )
         }
       }
+    },
+    then() {
+      return new Promise(res => {
+        this.once(data => {
+          res(data)
+        })
+      })
     }
   }
 }

utils/GunSmith/GunT.ts

@@ -70,6 +70,7 @@ namespace GunT {
     user(pub: string): GUNNode
     put(data: ValidDataValue, cb?: Callback): GUNNode
     set(data: ValidDataValue, cb?: Callback): GUNNode
+    then(): Promise<ListenerData>
   }
 
   export interface CreateAck {