Fixed #26013 -- Moved django.core.urlresolvers to django.urls.

Thanks to Tim Graham for the review.

docs/ref/class-based-views/generic-date-based.txt

@@ -13,7 +13,7 @@ views for displaying drilldown pages for date-based data.
     defined as follows in ``myapp/models.py``::
 
         from django.db import models
-        from django.core.urlresolvers import reverse
+        from django.urls import reverse
 
         class Article(models.Model):
             title = models.CharField(max_length=200)

docs/ref/class-based-views/generic-editing.txt

@@ -15,7 +15,7 @@ editing content:
     Some of the examples on this page assume that an ``Author`` model has been
     defined as follows in ``myapp/models.py``::
 
-        from django.core.urlresolvers import reverse
+        from django.urls import reverse
         from django.db import models
 
         class Author(models.Model):
@@ -227,7 +227,7 @@ DeleteView
     **Example myapp/views.py**::
 
         from django.views.generic.edit import DeleteView
-        from django.core.urlresolvers import reverse_lazy
+        from django.urls import reverse_lazy
         from myapp.models import Author
 
         class AuthorDelete(DeleteView):