Outdated py-evm version in Guide Doc: 'FrontierState' object has no attribute 'get_balance'

[junning-tong]

• OS: macOS 11.2.2
• Python Version (python --version): Python 3.6.13

What is wrong?

1. Guide Doc building_an_app_that_uses_pyevm is outdated, py-evm old version 0.2.0a40 causes script below to fail.

chain.get_vm().state.get_balance(MOCK_ADDRESS)

2. "Edit on GitHub" link redirects to 404 page.

https://py-evm.readthedocs.io/en/latest/guides/building_an_app_that_uses_pyevm.html

How can it be fixed

Update py-evm in doc to the latest version "py-evm==0.3.0a20"
https://github.com/ethereum/py-evm/blob/master/docs/guides/building_an_app_that_uses_pyevm.rst