Ignore vulnerability in hyper (#2188)

## Issue Addressed

NA

## Proposed Changes

Ignores a [hyper vuln](https://rustsec.org/advisories/RUSTSEC-2021-0020) that will be fixed in #2172.

I am comfortable with ignoring this because we have a fix in the works and the impact of the vuln is low to negligible.   

## Additional Info

NA

Makefile

@@ -137,7 +137,7 @@ arbitrary-fuzz:
 audit:
 	cargo install --force cargo-audit
 	# TODO: we should address this --ignore.
-	cargo audit --ignore RUSTSEC-2016-0002 --ignore RUSTSEC-2020-0008 --ignore RUSTSEC-2017-0002
+	cargo audit --ignore RUSTSEC-2016-0002 --ignore RUSTSEC-2020-0008 --ignore RUSTSEC-2017-0002 --ignore RUSTSEC-2021-0020
 
 # Runs `cargo udeps` to check for unused dependencies
 udeps: