Bump protobuf from 3.2.0 to 3.15.0 in /tools (#778)

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.2.0 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/compare/v3.2.0...v3.15.0)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

tools/setup.py

@@ -30,7 +30,7 @@ setup(name="mcsema-disass",
       author_email="mcsema@trailofbits.com",
       license='AGPLv3',
       packages=['mcsema_disass', 'mcsema_disass.ida7', 'mcsema_disass.defs'],
-      install_requires=['protobuf==3.2.0', 'python-magic'],
+      install_requires=['protobuf==3.15.0', 'python-magic'],
       package_data={
         "mcsema_disass.defs": ["linux.txt", "windows.txt"]},
       entry_points={