fuzz: update libfuzzer dependency
fuzz: update libfuzzer dependency

This is intended to fix an OSS-fuzz build failure detailed here:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=32817

Fixes #757 
rust-lang-nursery/regex,rust-lang-nursery/regex,rust-lang/regex,rust-lang/regex,rust-lang-nursery/regex,rust-lang/regex,rust-lang/regex,rust-lang-nursery/regex,rust-lang/regex,rust-lang-nursery/regex