Fix compile error with bson_free that should be bson_free_func.
Fix compile error with bson_free that should be bson_free_func.

mongodb/mongo-c-driver-legacy,mongodb/mongo-c-driver-legacy,HeliumProject/mongo-c,HeliumProject/mongo-c,Elastica/mongo-c-driver-legacy,Elastica/mongo-c-driver-legacy,mongodb/mongo-c-driver-legacy,mongodb/mongo-c-driver-legacy,HeliumProject/mongo-c,Elastica/mongo-c-driver-legacy,HeliumProject/mongo-c,Elastica/mongo-c-driver-legacy