Fixed docs build with sphinxcontrib-spelling 7.5.0+.

sphinxcontrib-spelling 7.5.0+ includes captions of figures in the set
of nodes for which the text is checked.

docs/topics/auth/passwords.txt

@@ -343,7 +343,7 @@ modify the pattern to work with any algorithm or with a custom user model.
 First, we'll add the custom hasher:
 
 .. code-block:: python
-    :caption: accounts/hashers.py
+    :caption: ``accounts/hashers.py``
 
     from django.contrib.auth.hashers import (
         PBKDF2PasswordHasher, SHA1PasswordHasher,
@@ -363,7 +363,7 @@ First, we'll add the custom hasher:
 The data migration might look something like:
 
 .. code-block:: python
-    :caption: accounts/migrations/0002_migrate_sha1_passwords.py
+    :caption: ``accounts/migrations/0002_migrate_sha1_passwords.py``
 
     from django.db import migrations
 
@@ -398,7 +398,7 @@ several thousand users, depending on the speed of your hardware.
 Finally, we'll add a :setting:`PASSWORD_HASHERS` setting:
 
 .. code-block:: python
-    :caption: mysite/settings.py
+    :caption: ``mysite/settings.py``
 
     PASSWORD_HASHERS = [
         'django.contrib.auth.hashers.PBKDF2PasswordHasher',