Protoc Rust update

[jmwample]

The signaling.rs file generated by protoc in the station code includes the use of inner attributes which are marked unstable in rust 1.52.1 and give an error at compile time.

When available, update the version of protoc so the manual fix from PR #89 is no longer required.

error: custom inner attributes are unstable
 --> src/signalling.rs:9:4
  |
9 | #![rustfmt::skip]
  |    ^^^^^^^^^^^^^
  |
  = note: `#[deny(soft_unstable)]` on by default
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>

error: aborting due to previous error

error: could not compile `rust_dark_decoy`