docs: change is prop to is attribute (#1236)

Author: Yukon123

src/guide/migration/introduction.md

@@ -93,7 +93,7 @@ The following consists a list of breaking changes from 2.x:
 ### Custom Elements
 
 - [Custom element checks are now performed during template compilation](/guide/migration/custom-elements-interop.html)
-- [Special `is` prop usage is restricted to the reserved `<component>` tag only](/guide/migration/custom-elements-interop.html#customized-built-in-elements)
+- [Special `is` attribute usage is restricted to the reserved `<component>` tag only](/guide/migration/custom-elements-interop.html#customized-built-in-elements)
 
 ### Other Minor Changes