rust 1.53.0 updates (#2411)

## Issue Addressed

`make lint` failing on rust 1.53.0.

## Proposed Changes

1.53.0 updates

## Additional Info

I haven't figure out why yet, we were now hitting the recursion limit in a few crates. So I had to add `#![recursion_limit = "256"]` in a few places


Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: Michael Sproul <michael@sigmaprime.io>

account_manager/src/validator/create.rs

@@ -236,7 +236,7 @@ pub fn cli_run<T: EthSpec>(
             .map_err(|e| {
                 format!(
                     "Error registering validator {}: {:?}",
-                    voting_pubkey.to_hex_string(),
+                    voting_pubkey.as_hex_string(),
                     e
                 )
             })?;
@@ -250,7 +250,7 @@ pub fn cli_run<T: EthSpec>(
             .build()
             .map_err(|e| format!("Unable to build validator directory: {:?}", e))?;
 
-        println!("{}/{}\t{}", i + 1, n, voting_pubkey.to_hex_string());
+        println!("{}/{}\t{}", i + 1, n, voting_pubkey.as_hex_string());
     }
 
     Ok(())