minor #11823 Fix broken link to doctrine documentation (mkopinsky)

This PR was submitted for the 4.3 branch but it was merged into the 3.4 branch instead (closes #11823).

Discussion
----------

Fix broken link to doctrine documentation

Commits
-------

773d015 Fix broken link to doctrine documentation

Author: javiereguiluz

form/form_collections.rst

@@ -715,6 +715,6 @@ the relationship between the removed ``Tag`` and ``Task`` object.
     elements of the collection. More advanced functionality like moving or duplicating
     an element in the collection and customizing the buttons is also possible.
 
-.. _`Owning Side and Inverse Side`: http://docs.doctrine-project.org/en/latest/reference/unitofwork-associations.html
+.. _`Owning Side and Inverse Side`: https://www.doctrine-project.org/projects/doctrine-orm/en/current/reference/unitofwork-associations.html
 .. _`JSFiddle`: http://jsfiddle.net/847Kf/4/
 .. _`symfony-collection`: https://github.com/ninsuo/symfony-collection