Update XmlDocument.xml (#4722)

fix typo DocumenType -> DocumentType

Author: hilvarenbeek

xml/System.Xml/XmlDocument.xml

@@ -2610,7 +2610,7 @@ elem=doc.CreateElement("xy", "item", "urn:abc");
 |XmlDeclaration|Copies the target and data value from the imported node.|Copies the target and data value from the imported node.|  
 |All other node types.|These node types cannot be imported.|These node types cannot be imported.|  
   
- *Although DocumentType nodes can be imported, a document can only have one DocumentType. If the document currently has a DocumenType node, it must be removed before adding a new one.  
+ *Although DocumentType nodes can be imported, a document can only have one DocumentType. If the document currently has a DocumentType node, it must be removed before adding a new one.