update README

Author: mfornaciari

README.md

@@ -1718,8 +1718,8 @@ In order to achieve greater coverage and encourage more people to contribute to
                 </a>
             </td>
             <td> <!-- Ruby -->
-                <a href="./CONTRIBUTING.md">
-                    <img align="center" height="25" src="./logos/github.svg" />
+                <a href="./src/ruby/binary_tree.rb">
+                    <img align="center" height="25" src="./logos/ruby.svg" />
                 </a>
             </td>
             <td> <!-- JavaScript -->