protoc no longer builds in 3.0.0 because auto-download of the gmock zip
now fails. 3.0.2 has a fix to autogen:
bba446bbf2
All that was strictly necessary was to update .travis.yml and
buildscripts/, but it helps our sanity to keep the rest of the protobuf
versions in sync. Lite is left on its existing version, because it did
not see a bump of neither the java library nor the protoc plugin.
This allows us to play with zero-copy and proto3 support for lite.
Unfortunately, it introduced some warnings, so deprecated warnings are
now ignored for benchmarks and interop-testing.