Unbreak parity-rpc build on rust -stable

[reyk]

   Compiling parity-rpc v1.12.0 (file:///home/reyk/devel/parity-ethereum/rpc)
error[E0658]: access to extern crates through prelude is experimental (see issue #44660)
   --> rpc/src/v1/helpers/light_fetch.rs:628:19
    |
628 |                         if let Some(vm::Error::OutOfGas) = executed.exception {
    |                                     ^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.
error: Could not compile `parity-rpc`.

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[reyk]

[clabot:check]

[parity-cla-bot]

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Many thanks,

Parity Technologies CLA Bot

[niklasad1]

Hey, thanks but it works on Rust stable 1.30. Please update your toolchain instead

[reyk]

It's a simple fix that works on both versions, what speaks against merging it?

I'm using OpenBSD 6.4 that ships rust 1.29.2 - OpenBSD -current includes 1.30.x or later but the next OpenBSD -stable release (6.5) will only be released in about 6 months.

[niklasad1]

Ok, didn't know that about OpenBSD!

Looks good, but we can't guarantee that we won't break it because rust 1.30 has some nice new features!

[reyk]

Thanks!