Bump hybrid-array to v0.4

[tarcieri]

Currently getting a test failure(!) in dsa, possibly related to crypto-bigint changes?

---- verify_signature stdout ----

thread 'verify_signature' panicked at dsa/tests/signature.rs:91:5:
assertion failed: verifying_key.verify_digest(Sha256::new().chain_update(MESSAGE),
        &signature).is_ok()
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- sign_message stdout ----

thread 'sign_message' panicked at dsa/tests/signature.rs:80:5:
assertion `left == right` failed
  left: Signature { r: NonZero(BoxedUint(0x00000000C6639F3AC90E4AAE648FB30C885F96A0C5E32D09)), s: NonZero(BoxedUint(0x00000000BFF0252CE80AC9281C12395433CA2FEC8A0DAAFF)) }
 right: Signature { r: NonZero(BoxedUint(0x000000004E12277518F640E33ADB806DE798D3A340F59D0F)), s: NonZero(BoxedUint(0x0000000017781EC8535891E03F2D3627366BAC8ED7F9A4CF)) }

Edit: confirm this test failure appears when updating crypto-bigint alone, going to bisect the changes.

Edit again: bisected to RustCrypto/crypto-bigint#920