Bump protobuf from 3.6.1 to 3.18.3

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.6.1 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/v3.6.1...v3.18.3)

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

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

requirements.txt

@@ -27,7 +27,7 @@ opencv-python==3.4.2.17
 pafy==0.5.4
 pandas==0.23.4
 Pillow==5.2.0
-protobuf==3.6.1
+protobuf==3.18.3
 psycopg2==2.7.5
 pyparsing==2.3.0
 python-dateutil==2.7.5