bug #12249 fix word: domain => subdomain (samayo)

This PR was merged into the 4.3 branch.

Discussion
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fix word: domain => subdomain

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Commits
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188861a fix word: domain => subdomain

Author: OskarStark

routing.rst

@@ -1635,7 +1635,7 @@ multi-tenant applications) and these parameters can be validated too with
             ;
         };
 
-In the above example, the ``domain`` parameter defines a default value because
+In the above example, the ``subdomain`` parameter defines a default value because
 otherwise you need to include a domain value each time you generate a URL using
 these routes.