Rename plugins to libs and update all file references

libs/stripe-php/lib/Exception/UnknownApiErrorException.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Stripe\Exception;
+
+/**
+ * UnknownApiErrorException is thrown when the client library receives an
+ * error from the API it doesn't know about. Receiving this error usually
+ * means that your client library is outdated and should be upgraded.
+ */
+class UnknownApiErrorException extends ApiErrorException {}