Bump protobuf from 3.7.1 to 3.18.3

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.7.1 to 3.18.3.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/generate_changelog.py)
- [Commits](https://github.com/protocolbuffers/protobuf/compare/v3.7.1...v3.18.3)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-type: direct:production
...

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

requirements.txt

@@ -1,6 +1,6 @@
 numpy==1.16.2
 Pillow==6.0.0
-protobuf==3.7.1
+protobuf==3.18.3
 six==1.12.0
 tensorboardX==1.6
 tqdm==4.31.1