Rename TikTok.php for psr-4 compatibility

[dhensby]

#347 introduced the TikTok oembed provider but the filename has a capital I which is not in compliance with the PSR-4 loading standard.

This causes a deprecation warning in composer as this class will not be autoloaded in composer v2

[oscarotero]

In fact, the class name should be Tiktok (with only the first letter as upper case), because this is the way getClassForDomain() function generates the class name to discover the Oembed configuration for a specific site (https://github.com/oscarotero/Embed/blob/v3.x/src/Providers/OEmbed.php#L188)

This code works in macOS and windows because their filesystems are case insensitive, but in Linux it won't work.

[dhensby]

OK - I've renamed the file and class now

[oscarotero]

Thanks