Use consistent term [skip ci]

guides/source/active_support_core_extensions.md

@@ -2349,7 +2349,7 @@ Contributor.limit(2).order(:rank).to_xml
 
 To do so it sends `to_xml` to every item in turn, and collects the results under a root node. All items must respond to `to_xml`, an exception is raised otherwise.
 
-By default, the name of the root element is the underscorized and dasherized plural of the name of the class of the first item, provided the rest of elements belong to that type (checked with `is_a?`) and they are not hashes. In the example above that's "contributors".
+By default, the name of the root element is the underscored and dasherized plural of the name of the class of the first item, provided the rest of elements belong to that type (checked with `is_a?`) and they are not hashes. In the example above that's "contributors".
 
 If there's any element that does not belong to the type of the first one the root node becomes "objects":