Update CLA URL

Author: mkuratczyk

CONTRIBUTING.md

@@ -13,7 +13,7 @@ The process is fairly standard:
  * Create a branch with a descriptive name in the relevant repositories
  * Make your changes, run tests, commit with a [descriptive message](https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html), push to your fork
  * Submit pull requests with an explanation what has been changed and **why**
- * Submit a filled out and signed [Contributor Agreement](https://github.com/rabbitmq/ca#how-to-submit) if needed (see below)
+ * Submit a filled out and signed [Contributor Agreement](https://cla.pivotal.io) if needed (see below)
  * Be patient. We will get to your pull request eventually
 
 If what you are going to work on is a substantial change, please first ask the core team
@@ -28,7 +28,7 @@ See [CODE_OF_CONDUCT.md](./CODE_OF_CONDUCT.md).
 ## Contributor Agreement
 
 If you want to contribute a non-trivial change, please submit a signed copy of our
-[Contributor Agreement](https://github.com/rabbitmq/ca#how-to-submit) around the time
+[Contributor Agreement](https://cla.pivotal.io/) around the time
 you submit your pull request. This will make it much easier (in some cases, possible)
 for the RabbitMQ team at Pivotal to merge your contribution.