Support wasm use cases by removing time crate dependency

[pfernie]

As discussing in this reqwest issue, the transitive dependency on the time crate causes issues when targeting wasm. The upstream cookie-rs crate has a dependency here as well, so supporting this use case would involve an upstream change as well.

[jhpratt]

The time crate will support wasm via js-sys soon! There's an open PR.

[xy2i]

time-rs/time#491

[jkelleyrtp]

The PR is up here #27 - would love to see this supported so I can move seanmonstar/reqwest#1449 forward

[pfernie]

#27 has been merged; I am leaving this issue open pending feedback that seanmonstar/reqwest#1449 can move forward with this change, at which point I can cut a 0.18.0 release including the change.