Update app.py

app.py

@@ -51,8 +51,8 @@ def display_chain():
     return response
     
 def mine_block(chain_r=None,chain_n=None):
-    if chain_name=="":
-        chain_name = chain_d
+    if chain_n=="":
+        chain_n = chain_d
     previous_block = blockchain.print_previous_block()
     previous_proof = previous_block['proof']
     proof = blockchain.proof_of_work(previous_proof)