Fix coverage reporting to coveralls.io

Reproduced on [Travis-CI][1]:

> [ERROR] Failed to execute goal org.eluder.coveralls:coveralls-maven-plugin:4.3.0:report (default-cli) on project connector: I/O operation failed: No source found for org/tarantool/Version.java -> [Help 1]

[1]: https://travis-ci.org/tarantool/tarantool-java/jobs/509400247#L3200

I think we should exclude generated sources from jacoco statistics.