Fix unserialize() error when using Redis as cache (#30)

* Fix unserialize(): Error at offset when using Redis as cache

Using the key `disposable_email.domains` in Redis throw an error `unserialize(): Error at offset XYZ of XYZ bytes`, Redis cannot unserialize keys with dot notation. I think is better to replace the key with underscore so it works in most cache drivers.

* Update disposable-email.php

Co-authored-by: Propaganistas <[email protected]>

config/disposable-email.php

@@ -64,7 +64,7 @@
     'cache' => [
         'enabled' => true,
         'store' => 'default',
-        'key' => 'disposable_email.domains',
+        'key' => 'disposable_email:domains',
     ],
 
 ];