Fix link to CONTRIBUTING.md

doc/07-community.md

@@ -6,8 +6,8 @@ contributing.
 ## Contributing
 
 If you would like to contribute to Composer, please read the
-[README](https://github.com/composer/composer) and 
-[CONTRIBUTING](https://github.com//composer/composer/blob/master/CONTRIBUTING.md)
+[README](https://github.com/composer/composer) and
+[CONTRIBUTING](https://github.com//composer/composer/blob/master/.github/CONTRIBUTING.md)
 documents.
 
 The most important guidelines are described as follows: