Add ext-curl to list of dependencies

[Xartrick]

Missing PHP extension curl should be detected on installation.

$ composer require alaouy/youtube
Using version ^2.2 for alaouy/youtube
./composer.json has been updated
Running composer update alaouy/youtube
Loading composer repositories with package information
Updating dependencies
Lock file operations: 1 install, 0 updates, 0 removals
  - Locking alaouy/youtube (v2.2.4)
Writing lock file
Installing dependencies from lock file (including require-dev)
Package operations: 1 install, 0 updates, 0 removals
  - Installing alaouy/youtube (v2.2.4): Extracting archive
[..]

$ php artisan tinker
Psy Shell v0.10.4 (PHP 7.4.12 — cli) by Justin Hileman
>>> Youtube::getChannelById('UCcdNy_FqMi0z1VU6kanOvFQ')
PHP Error:  Call to undefined function Alaouy/Youtube/curl_init() in REDACTED/vendor/alaouy/youtube/src/Youtube.php on line 738

[alaouy]

@Xartrick Thank you (y )