Bump protobuf from 2.22.1 to 3.4.0

Bumps [protobuf](https://github.com/stepancheg/rust-protobuf) from 2.22.1 to 3.4.0.
- [Changelog](https://github.com/stepancheg/rust-protobuf/blob/master/CHANGELOG-before-3.md)
- [Commits](stepancheg/rust-protobuf@v2.22.1...v3.4.0)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

intel-sgx/aesm-client/Cargo.toml

@@ -32,7 +32,7 @@ sgx-isa = { version = "0.4.0", path = "../sgx-isa"}
 # External dependencies
 byteorder = "1.0"          # Unlicense/MIT
 lazy_static = "1"          # MIT/Apache-2.0
-protobuf = "2.22.1"        # MIT/Apache-2.0
+protobuf = "3.4.0"        # MIT/Apache-2.0
 thiserror = "1.0"          # MIT/Apache-2.0
 anyhow = "1.0"             # MIT/Apache-2.0