Client CPP 3.1.1

What's Changed

• Fix segfault caused by socket I/O on a closed io_service by @BewareMyPower in https://github.com/apache/pulsar-client-cpp/pull/168
• [fix][build] Hide non-exported symbols from the dependencies by @BewareMyPower in https://github.com/apache/pulsar-client-cpp/pull/155
• [fix] Use authoritative argument correctly in BinaryProtoLookupService::findBroker by @erobot in https://github.com/apache/pulsar-client-cpp/pull/146
• [fix] Fix a crash when closing a connection while connecting by @erobot in https://github.com/apache/pulsar-client-cpp/pull/136
• [fix] Close broker producer created after producer close by @erobot in https://github.com/apache/pulsar-client-cpp/pull/131
• [fix] Fix hostname verification by @izumo27 in https://github.com/apache/pulsar-client-cpp/pull/126

Full Changelog: https://github.com/apache/pulsar-client-cpp/compare/v3.1.0...v3.1.1