Fix typo in MP_Node.fix_tree doc
Fix typo in MP_Node.fix_tree doc

--HG--
branch : fix-typo

albedoweb/django-treebeard,albedoweb/django-treebeard,velfimov/django-treebeard,velfimov/django-treebeard,albedoweb/django-treebeard,albedoweb/django-treebeard,velfimov/django-treebeard,velfimov/django-treebeard