上游提案修正 /pull/8

> 在英文书 Mastering Ethereum 里，是使用 Data structures 而不是 Blockchain
Data structures
Ethereum's state is stored locally on each node as a database (usually Google's LevelDB), which contains the transactions and system state in a serialized hashed data structure called a Merkle Patricia Tree.

https://github.com/inoutcode/ethereum_book/pull/8