chore: fix typo in provider readme

supersedes gakonst/ethers-rs#1203

ethers-providers/README.md

@@ -10,6 +10,7 @@ For more documentation on the available calls, refer to the
 # Examples
 
 ```no_run
+use ethers_core::types::Address;
 use ethers_providers::{Provider, Http, Middleware};
 use std::convert::TryFrom;
 
@@ -21,7 +22,8 @@ let provider = Provider::<Http>::try_from(
 let block = provider.get_block(100u64).await?;
 println!("Got block: {}", serde_json::to_string(&block)?);
 
-let code = provider.get_code("0x89d24a6b4ccb1b6faa2625fe562bdd9a23260359", None).await?;
+let addr = "0x89d24a6b4ccb1b6faa2625fe562bdd9a23260359".parse::<Address>()?;
+let code = provider.get_code(addr, None).await?;
 println!("Got code: {}", serde_json::to_string(&code)?);
 # Ok(())
 # }