Fix redirect links

Author: stevepiercy

docs/backend/upgrading/version-specific-migration/p4x-to-p5x-upgrade.md

@@ -74,7 +74,7 @@ When the email addresses are not unique, for example you have both `joe@example.
 It is best is to fix this in your site in Plone 4
 Change email addresses or remove no longer needed users.
 When there are only a few users, you can do this manually.
-To assist you in sites with many users, in Plone 4.1 and higher, you can add the [collective.emaillogin4](https://pypi.python.org/pypi/collective.emaillogin4) package to the eggs of your Plone instance.
+To assist you in sites with many users, in Plone 4.1 and higher, you can add the [collective.emaillogin4](https://pypi.org/project/collective.emaillogin4) package to the eggs of your Plone instance.
 
 With that package, even without installing it in the add-ons control panel, you can call the `@@migrate-to-emaillogin` page to look for duplicate email addresses.
 
@@ -272,7 +272,7 @@ An old style Resource Registry would look like this:
 </object>
 ```
 
-To migrate this to Plone 5, resource registrations are all done in the [Configuration Registry](https://pypi.python.org/pypi/plone.app.registry).
+To migrate this to Plone 5, resource registrations are all done in the [Configuration Registry](https://pypi.org/project/plone.app.registry).
 
 
 #### New style with {file}`registry.xml`

docs/backend/upgrading/version-specific-migration/upgrade-to-51.md

@@ -279,7 +279,7 @@ Adding or editing a document is faster, because care was taken to avoid duplicat
 
 #### For Developers
 
-The [collective.indexing](https://pypi.python.org/pypi/collective.indexing) package was merged into the core of Plone.
+The [collective.indexing](https://pypi.org/project/collective.indexing) package was merged into the core of Plone.
 This makes sure that objects are only indexed once per transaction.
 
 It also gives hooks for calling external indexers, like Solr and Elasticsearch.

docs/backend/upgrading/version-specific-migration/upgrade-to-python3.md

@@ -26,7 +26,7 @@ If you want to upgrade add-ons to Python 3, the list of all Plone packages that
 
 - You should support Python 2 and 3 with the same codebase to allow it to be used in existing versions of Plone.
 - Plone 5.2 supports Python 2.7, Python 3.6, and Python 3.7.
-- We use [six](https://six.readthedocs.io) and [modernize](https://pypi.python.org/pypi/modernize) to do the first steps towards Python 3.
+- We use [six](https://six.readthedocs.io) and [modernize](https://pypi.org/project/modernize) to do the first steps towards Python 3.
 
 In general you should follow these steps to port add-ons:
 
@@ -154,7 +154,7 @@ Check this [Cheat Sheet](http://python-future.org/compatible_idioms.html)  with
 
 `python-modernize` adds an import of the compatibility library `six` if needed.
 The import is added as the last import, therefore it is often necessary to reorder the imports.
-The easiest way is to use [isort](https://pypi.python.org/pypi/isort), which does this for you automatically.
+The easiest way is to use [isort](https://pypi.org/project/isort), which does this for you automatically.
 Check the [Python style guide for Plone](https://docs.plone.org/develop/styleguide/python.html#grouping-and-sorting) for information about the order of imports and an example configuration for `isort`.
 
 If `six` is used in the code, make sure that `six` is added to the `install_requires` list in the `setup.py` of the package.