Update app.py

app.py

@@ -273,7 +273,7 @@ def mychain_mine_block_send(balance, chain_r=None,chain_n=None):
 
     previous_post = mychain_send.print_previous_block()
     
-    block = {'index': previous_post[['index'],
+    block = {'index': previous_post['index'],
             'timestamp': previous_post['timestamp'],
             'sender': previous_post['transactions'][0]['sender'],
             'recipient': previous_post['transactions'][0]['recipient'],