Bump rust-gmp to 0.3 to fix build on nightly rustc

[petrochenkov]

Hi.
rust-lang/rust#42125 is going to turn some old compatibility "private-in-public" warnings in rustc into hard errors.
crates.io testing discovered that this crate uses an old version of rust-gmp affected by one of those errors.
This PR updates rust-gmp to 0.3, which is the minimal version building successfully with rust-lang/rust#42125

[hwchen]

Thanks! Will merge shortly.

[petrochenkov]

@hwchen
Could you also publish the updated version to crates.io as secret-service-0.3.2?

[hwchen]

Yup, getting to it this morning, didn't have quite enough time last night. Thanks! On Jun 6, 2017 4:46 AM, "Vadim Petrochenkov" <[email protected]> wrote: @hwchen <https://github.com/hwchen> Could you also publish the updated version to crates.io as secret-service-0.3.2? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#2 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ADm0i44LAiKyHpWEN8ru8FNjew4u-HZoks5sBRHwgaJpZM4NoUTj> .

[hwchen]

published! as 0.4.0, because of a more major change in #1

[petrochenkov]

Thanks!