Revert "Update criterion requirement from 0.4 to 0.5" (#150)

This reverts commit 236d5a6.

Author: taiki-e

Cargo.toml

@@ -43,7 +43,7 @@ autocfg = "1"
 async-channel = "1"
 async-net = "1"
 blocking = "1"
-criterion = { version = "0.5", default-features = false, features = ["cargo_bench_support"] }
+criterion = { version = "0.4", default-features = false, features = ["cargo_bench_support"] }
 getrandom = "0.2.7"
 signal-hook = "0.3"
 tempfile = "3"