ethkey doesnt compile as a Cargo dependency

[felipeargento]

Before filing a new issue, please provide the following information.

• Parity Ethereum version: 2.5.5
• Operating system: Linux

actual:
Building parity-ethereum as a Cargo dependency on either master or stable branch fails with the following error - while compiling ethkey (v0.3.0):

error[E0277]: the trait bound rand::OsRng: secp256k1::rand::RngCore is not satisfied

Cloning the repository and using Cargo build directly on it is successful, but adding it to another projects Cargo.toml as a dependency produces this error.

expected behavior:
Should be able to compile normally as a cargo dependency without any errors.

steps to reproduce:

• Create a dummy project.
• Add a Cargo.toml with ethkey = { git = "https://github.com/cartesi/parity-ethereum", branch = "stable" } dependency.
• Add lib.rs with extern crate ethkey;.
• Run Cargo build

how to fix:
Modify eth-secp256k1 inside accounts/ethkey/Cargo.toml:
Change:
eth-secp256k1 = { git = "https://github.com/paritytech/rust-secp256k1" }
To:
eth-secp256k1 = { git = "https://github.com/paritytech/rust-secp256k1", rev = "ccc06e7" }

[ordian]

@felipeargento parity-ethereum master (and beta) branch uses the rand 0.6 and hence the latest revision of eth-secp256k1 (https://github.com/paritytech/parity-ethereum/blob/14e7641835f2ece9d9fef66e6be53cce360d9c53/Cargo.lock#L776). For stable branch, a revision of eth-secp256k1 is fixed inside of the Cargo.lock. We could add a rev to stable branch though to make it work for lib crates that depend on stable branch.

[niklasad1]

Fixed by #11239