Bump discv5 to v0.1.0-beta.8 (#2471)

## Proposed Changes

Update discv5 to fix bugs seen on `altair-devnet-1`

Author: michaelsproul

Cargo.lock

@@ -5,7 +5,7 @@ authors = ["Sigma Prime <[email protected]>"]
 edition = "2018"
 
 [dependencies]
-discv5 = { version = "0.1.0-beta.7", features = ["libp2p"] }
+discv5 = { version = "0.1.0-beta.8", features = ["libp2p"] }
 unsigned-varint = { version = "0.6.0", features = ["codec"] }
 types = { path =  "../../consensus/types" }
 hashset_delay = { path = "../../common/hashset_delay" }