Steps to update the protobuf library version:
Start by finding a protobuf library version released to Maven Central that has functionality you need, e.g. nano. See http://mvnrepository.com/artifact/com.google.protobuf.
Update the protobuf library dependency's groupId, artifactId, and version to match this
artifact in all the pom.xml files. You can find the files by searching for
<groupId>com.google.protobuf in the GitHub repository.
Download the .jar from the Maven Repository,
e.g. from http://repo1.maven.org/maven2/com/google/protobuf/nano/protobuf-javanano/3.0.0-alpha-7/,
and copy to java/lib/, replacing the previous version's .jar.
See https://github.com/google/protobuf/releases for the release containing the chosen version, and
download the protoc binary for your machine's architecture from the same release and use this to
re-generate java/libphonenumber/src/com/google/i18n/phonenumbers/nano/Phonemetadata.java and
check in any changes to this file. The command from the root directory is:
protoc --javanano_out=com.google.i18n.phonenumbers.nano:java/libphonenumber/src \
resources/phonemetadata.proto \
--proto_path=resources