Fix error[E0008]: cannot bind by-move into a pattern guard

[froody]

Fixes the following error:

Error: error[E0008]: cannot bind by-move into a pattern guard
--> src/net/driver/mod.rs:207:17
|
207 | Err(err) if err.kind() == io::ErrorKind::WouldBlock => {}
| ^^^ moves value into pattern guard
|
= help: add #![feature(bind_by_move_pattern_guards)] to the crate attributes to enable

[taiki-e]

As bind_by_move_pattern_guards stabilized about two weeks ago (rust-lang/rust#63118), I believe updating the version of rustc should fix this error.

[ghost]

@froody what is your rustc version?

[froody]

@stjepang 1.38, updating to 1.39 isn't really feasible right now

[yoshuawuyts]

We haven't quite talked about this internally, but given nobody on the team has really moved to act on this PR I think there's a silent consensus that we're not targeting any versions of the compiler under 1.39.

We probably should still formulate our support strategy in the face of the upcoming stabilization of async/await. I suspect it'll be something like: "always work on stable; only conditionally support new nightly features".

Either way, I don't want to keep this PR open indefinitely so I'm going to go ahead and close this. Thanks heaps!