Update README.md Fixes broken Cache Interface link

Author: adampatterson

README.md

@@ -252,7 +252,7 @@ $client = new IPinfo($access_token, $settings);
 
 #### Using a different cache
 
-It's possible to use a custom cache by creating a child class of the [CacheInterface](https://github.com/ipinfo/php/blob/master/src/cache/Interface.php) class and passing this into the handler object with the `cache` keyword argument. FYI this is known as [the Strategy Pattern](https://sourcemaking.com/design_patterns/strategy).
+It's possible to use a custom cache by creating a child class of the [CacheInterface](https://github.com/ipinfo/php/blob/master/src/cache/CacheInterface.php) class and passing this into the handler object with the `cache` keyword argument. FYI this is known as [the Strategy Pattern](https://sourcemaking.com/design_patterns/strategy).
 
 ```php
 $access_token = '123456789abc';