title: getTransactionReceipt() return None
body: <p><code>w3.eth.getTransactionReceipt(tx_hash)</code> function returns <code>None</code>.</p>
  
  <p>My code:</p>
  
  <pre><code>provider = HTTPProvider('http://0.0.0.0:9945')
  w3 = Web3(provider)
  
  contract = w3.eth.contract(contract_interface['abi'], bytecode=contract_interface['bin'])
  
  tx_hash = contract.deploy(transaction={'from': w3.eth.coinbase, 'gas': 250000})
  
  print (tx_hash)
  time.sleep(1)
  tx_receipt = w3.eth.getTransactionReceipt(tx_hash)
  print (tx_receipt)
  contract_address = tx_receipt['contractAddress']
  </code></pre>
  
  <p><code>tx_hash</code> is normal value but <code>tx_receipt</code> is <code>None</code>.</p>
  
  <p>So my error:</p>
  
  <pre><code>contract_address = tx_receipt['contractAddress']
  TypeError: 'NoneType' object is not subscriptable
  </code></pre>
  
  <p>How can I solve this?</p>