PHPLIB-538: Update comment in withTxn examples for the manual
PHPLIB-538: Update comment in withTxn examples for the manual

mongodb/mongo-php-library,mongodb/mongo-php-library,jmikola/mongo-php-library,jmikola/mongo-php-library,jmikola/mongo-php-library-prototype,jmikola/mongo-php-library,jmikola/mongo-php-library,mongodb/mongo-php-library,mongodb/mongo-php-library,10gen-labs/mongo-php-library-prototype