Make protobuf cleanup its resourced when servatrice ends

Should help make valgrind’s log a bit cleaner

servatrice/src/main.cpp

@@ -29,6 +29,7 @@
 #include "server_logger.h"
 #include "rng_sfmt.h"
 #include "version_string.h"
+#include <google/protobuf/stubs/common.h>
 #ifdef Q_OS_UNIX
 #include <signal.h>
 #endif
@@ -233,5 +234,8 @@ int main(int argc, char *argv[])
 	loggerThread->wait();
 	delete loggerThread;
 
+	// Delete all global objects allocated by libprotobuf.
+	google::protobuf::ShutdownProtobufLibrary();
+
 	return retval;
 }