Rename plugins to libs and update all file references

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

@@ -0,0 +1,10 @@
+<?php
+
+namespace Stripe\Exception;
+
+/**
+ * RateLimitException is thrown in cases where an account is putting too much
+ * load on Stripe's API servers (usually by performing too many requests).
+ * Please back off on request rate.
+ */
+class RateLimitException extends InvalidRequestException {}