fuzz: bump libfuzzer-sys dependency

This is a half-hearted attempt to fix a build failure that I don't
understand in OSS-fuzz:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=34294

cc @DavidKorczynski

Author: BurntSushi

Diff for: fuzz/Cargo.toml

@@ -11,7 +11,7 @@ edition = "2018"
 cargo-fuzz = true
 
 [dependencies]
-libfuzzer-sys = "0.4.0"
+libfuzzer-sys = "0.4.1"
 
 [dependencies.regex]
 path = ".."