Bump protobuf-java from 3.18.0 to 3.18.1

Bumps protobuf-java from 3.18.0 to 3.18.1.

Release notes

Sourced from protobuf-java's releases.

Protocol Buffers v3.18.1

Python

• Update setup.py to reflect that we now require at least Python 3.5 (#8989)
• Performance fix for DynamicMessage: force GetRaw() to be inlined (#9023)

Ruby

• Update ruby_generator.cc to allow proto2 imports in proto3 (#9003)

Commits

• 0dab03b Update protobuf version to 3.18.1 (#9051)
• 40f6669 Update changelog for 3.18.1 (#9050)
• aeb624d Avoid installing anything from Homebrew in test runs (#9043)
• bfc4c34 Merge pull request #9021 from acozzette/cherry-pick-fixes
• 5378c9a Use the stable version of rvm
• 55b0e11 Fix Ruby tests on Mac
• 0333cb7 Update ruby/travis-test.sh to print commands
• 0e7a35f Update dist_install test to work around Python issue
• bf8d7f0 Merge pull request #9023 from haberman/dyn-msg-perf-fix
• 5e8396f Performance fix for DynamicMessage: force GetRaw() to be inlined.
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