Bump protobuf from 3.5.2.post1 to 3.15.0 in /examples/cinc17/entry

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.5.2.post1 to 3.15.0.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/master/generate_changelog.py)
- [Commits](https://github.com/protocolbuffers/protobuf/commits/v3.15.0)

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

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

examples/cinc17/entry/requirements.txt

@@ -16,7 +16,7 @@ mock==2.0.0
 numpy==1.14.3
 pbr==4.0.4
 pip==10.0.1
-protobuf==3.5.2.post1
+protobuf==3.15.0
 PyYAML==3.12
 setuptools==39.2.0
 scipy==1.1.0