Upgrade async-sse to 5.1.0

Author: joshtriplett

Cargo.toml

@@ -35,7 +35,7 @@ unstable = []
 [dependencies]
 async-h1 = { version = "2.3.0", optional = true }
 async-session = { version = "3.0", optional = true }
-async-sse = "4.0.1"
+async-sse = "5.1.0"
 async-std = { version = "1.6.5", features = ["unstable"] }
 async-trait = "0.1.41"
 femme = { version = "2.1.1", optional = true }