Update to inherit from correct Faraday error

The update to Faraday is causing `require "octokit"` to break. Updating
to `Faraday::ClientError` fixes it and is correct based on Faraday code:
https://github.com/lostisland/faraday/blob/master/lib/faraday/error.rb

lib/octokit/middleware/follow_redirects.rb

@@ -11,7 +11,7 @@ module Octokit
   module Middleware
 
     # Public: Exception thrown when the maximum amount of requests is exceeded.
-    class RedirectLimitReached < Faraday::Error::ClientError
+    class RedirectLimitReached < Faraday::ClientError
       attr_reader :response
 
       def initialize(response)