You require the stable version (1.3.10) in your composer.json file, but your file is in steam-condenser-php-master/?
Additionally, your project's files do not belong into Steam Condenser's directory (or any library's directory for that matter).
Your code looks fine, but you might need some require statements.
And a last tip: Is your question really a GoldSrc server (old HL1 engine)? If not, please use SourceServer.
PS: Please do not post multiple (near) identical messages to this list.