mongo-php-driver: Unable to use mongodb+srv URI format

Description

I’m unable to use the URI string format mongo+srv to connect to my MongoDB cluster.

Environment

Driver (1.4.2) and ext-mongodb (1.5.3) are latest versions available. PHP is a Docker container, starting from the official Alpine image:

$ php -v
PHP 7.3.3 (cli) (built: Mar  9 2019 01:29:50) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.3, Copyright (c) 1998-2018 Zend Technologies
    with Zend OPcache v7.3.3, Copyright (c) 1999-2018, by Zend Technologies
    with Xdebug v2.7.0, Copyright (c) 2002-2019, by Derick Rethans
    with blackfire v1.24.4~linux-musl-x64-non_zts73, https://blackfire.io, by Blackfire

$ php -i | grep -E 'mongodb|libmongoc|libbson' 

/usr/local/etc/php/conf.d/docker-php-ext-mongodb.ini,
mongodb
libbson bundled version => 1.13.0
libmongoc bundled version => 1.13.0
libmongoc SSL => enabled
libmongoc SSL library => OpenSSL
libmongoc crypto => enabled
libmongoc crypto library => libcrypto
libmongoc crypto system profile => disabled
libmongoc SASL => enabled
libmongoc ICU => disabled
libmongoc compression => enabled
libmongoc compression snappy => disabled
libmongoc compression zlib => enabled
mongodb.debug => no value => no value

Test Script

<?php

require_once __DIR__ . '/vendor/autoload.php';

new \MongoDB\Client('mongodb+srv://mongo/');

Expected and Actual Behavior

Expected: no errors. Actual:

PHP Fatal error:  Uncaught MongoDB\Driver\Exception\InvalidArgumentException: Failed to parse MongoDB URI: 'mongodb+srv://mongo/'. Invalid service name in URI. in /var/www/insight/core/vendor/mongodb/mongodb/src/Client.php:87
Stack trace:
#0 /var/www/insight/core/vendor/mongodb/mongodb/src/Client.php(87): MongoDB\Driver\Manager->__construct('mongodb+srv://m...', Array, Array)
#1 /var/www/insight/core/test.php(5): MongoDB\Client->__construct('mongodb+srv://m...')
#2 {main}
  thrown in /var/www/insight/core/vendor/mongodb/mongodb/src/Client.php on line 87