Fix address of git remote for committers

`git clone` didn't work with `git@git.ruby-lang.org:ruby/ruby.git`, but it works with `git@git.ruby-lang.org:ruby.git`, so we better use the later here.

Author: duerst

en/community/ruby-core/index.md

@@ -39,7 +39,7 @@ If you have commit access, and if you want to push something,
 you should use the primary repository.
 
 {% highlight sh %}
-$ git clone git@git.ruby-lang.org:ruby/ruby.git
+$ git clone git@git.ruby-lang.org:ruby.git
 {% endhighlight %}
 
 ### Improving Ruby, Patch by Patch