docs: update key name strikethrough -> strike (#1589)

Author: brandonwie

docs/pages/docs/editor-basics/default-schema.mdx

@@ -195,7 +195,7 @@ type Styles = {
   bold: boolean;
   italic: boolean;
   underline: boolean;
-  strikethrough: boolean;
+  strike: boolean;
   textColor: string;
   backgroundColor: string;
 };