Correct documentation link

changed link from https://dev.metasploit.com/documents/api/ to https://dev.metasploit.com/api/

Author: firefart

CONTRIBUTING.md

@@ -50,7 +50,7 @@ Pull requests [#2940](https://github.com/rapid7/metasploit-framework/pull/2940)
 #### New Modules
 
 * **Do** run `tools/msftidy.rb` against your module and fix any errors or warnings that come up. Even better would be to set up `msftidy.rb` as a [pre-commit hook](https://github.com/rapid7/metasploit-framework/blob/master/tools/dev/pre-commit-hook.rb).
-* **Do** use the [many module mixin APIs](https://dev.metasploit.com/documents/api/). Wheel improvements are welcome; wheel reinventions, not so much.
+* **Do** use the [many module mixin APIs](https://dev.metasploit.com/api/). Wheel improvements are welcome; wheel reinventions, not so much.
 * **Don't** include more than one module per pull request.
 
 #### Library Code