docs(README): update README to use CLA assistant

README.md

@@ -99,7 +99,7 @@ Sadly (and ironically, given the the original need for this code: measuring the
 
 # Contributing
 
-We welcome Your interest in the American Express Open Source Community on Github. Any Contributor to any Open Source Project managed by the American Express Open Source Community must accept and sign an Agreement indicating agreement to the terms below. Except for the rights granted in this Agreement to American Express and to recipients of software distributed by American Express, You reserve all right, title, and interest, if any, in and to Your Contributions. Please [fill out the Agreement](http://goo.gl/forms/mIHWH1Dcuy).
+We welcome Your interest in the American Express Open Source Community on Github. Any Contributor to any Open Source Project managed by the American Express Open Source Community must accept and sign an Agreement indicating agreement to the terms below. Except for the rights granted in this Agreement to American Express and to recipients of software distributed by American Express, You reserve all right, title, and interest, if any, in and to Your Contributions. Please [fill out the Agreement](https://cla-assistant.io/americanexpress/).
 
 # License