update contributor link

Author: blink1073

CONTRIBUTING.rst

@@ -11,7 +11,7 @@ share what area of the project you are interested in working on.
 For general documentation about contributing to Jupyter projects, see the
 `Project Jupyter Contributor Documentation`__.
 
-__ https://jupyter.readthedocs.io/en/latest/contributor/content-contributor.html
+__ https://jupyter.readthedocs.io/en/latest/contributing/content-contributor.html
 
 Setting Up a Development Environment
 ====================================