chore(deps): bump spki from 0.5.4 to 0.6.0 (gakonst#1238)

Bumps [spki](https://github.com/RustCrypto/formats) from 0.5.4 to 0.6.0.
- [Release notes](https://github.com/RustCrypto/formats/releases)
- [Commits](RustCrypto/formats@spki/v0.5.4...spki/v0.6.0)

---
updated-dependencies:
- dependency-name: spki
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

ethers-signers/Cargo.toml

@@ -34,7 +34,7 @@ trezor-client = { version = "0.0.5", optional = true, default-features = false,
 rusoto_core = { version = "0.48.0", optional = true }
 rusoto_kms = { version = "0.48.0", optional = true }
 tracing = { version = "0.1.34", optional = true }
-spki = { version = "0.5.4", optional = true }
+spki = { version = "0.6.0", optional = true }
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 eth-keystore = { version = "0.4.1" }