Update app.py

app.py

@@ -354,7 +354,7 @@ def merge_trans():
             'amount': previous_post_rec['transactions'][0]['amount'],
             'balance': previous_post_rec['balance'], 
             'proof': previous_post_rec['proof'],
-            'previous_hash': previous_post_rec['previous_hash']}
+            'previous_hash': previous_post_rec['previous_hash'],
             'block': blockchain.print_previous_block()['index']+1}
 
     trans_bx.append(send_block)