Update CLA links and alias

Author: gtritchie

.github/CONTRIBUTING.md

@@ -4,7 +4,7 @@ To submit a contribution:
 
 1. [Fork](https://github.com/rstudio/leaflet/fork) the repository and make your changes.
 
-2. Ensure that you have signed the [individual](https://rstudioblog.files.wordpress.com/2017/05/rstudio_individual_contributor_agreement.pdf) or [corporate](https://rstudioblog.files.wordpress.com/2017/05/rstudio_corporate_contributor_agreement.pdf) contributor agreement as appropriate. You can send the signed copy to jj@rstudio.com.
+2. Ensure that you have signed the [individual](https://www.rstudio.com/wp-content/uploads/2014/06/rstudioindividualcontributoragreement.pdf) or [corporate](https://www.rstudio.com/wp-content/uploads/2014/06/rstudiocorporatecontributoragreement.pdf) contributor agreement as appropriate. You can send the signed copy to contribute@rstudio.com.
 
 3. Submit a [pull request](https://help.github.com/articles/using-pull-requests).