Bump protobuf from 3.7.0 to 3.11.3

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.7.0 to 3.11.3.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/master/generate_changelog.py)
- [Commits](protocolbuffers/protobuf@v3.7.0...v3.11.3)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

requirements.in

@@ -4,7 +4,7 @@ cffi>=1.13.0
 future==0.18.2
 itsdangerous==0.24
 pbr==1.10.0
-protobuf==3.7.0
+protobuf==3.11.3
 pyopenssl==18.0.0
 PyYAML==5.2 # PyYAML 5.3 does not support Python 3.4
 pytz==2018.9

requirements.txt

@@ -14,7 +14,7 @@ future==0.18.2            # via -r requirements.in
 idna==2.7                 # via requests
 itsdangerous==0.24        # via -r requirements.in
 pbr==1.10.0               # via -r requirements.in
-protobuf==3.7.0           # via -r requirements.in
+protobuf==3.11.3          # via -r requirements.in
 pycparser==2.18           # via cffi
 pyopenssl==18.0.0         # via -r requirements.in
 pytz==2018.9              # via -r requirements.in