Make the Expires header parse as a plain string
Make the Expires header parse as a plain string

Google is sending these headers with value '-1', which doesn't parse.

chris-morgan/rust-http,servo/rust-http,servo/rust-http,Shraddha512/rust-http,servo/rust-http,chris-morgan/rust-http,Shraddha512/rust-http,Shraddha512/rust-http,servo/rust-http,Shraddha512/rust-http,chris-morgan/rust-http,chris-morgan/rust-http,Shraddha512/rust-http