[3.7] Fix signature of xml.dom.minidom.Document.toprettyxml(). (GH-10814). (GH-10824)

(cherry picked from commit b7c2182604d5796b5af4c837991aa0b8c8a2d41f)
diff --git a/Doc/library/xml.dom.minidom.rst b/Doc/library/xml.dom.minidom.rst
index 40470e8..d5d7b20 100644
--- a/Doc/library/xml.dom.minidom.rst
+++ b/Doc/library/xml.dom.minidom.rst
@@ -156,7 +156,7 @@
    encoding. Encoding this string in an encoding other than UTF-8 is
    likely incorrect, since UTF-8 is the default encoding of XML.
 
-.. method:: Node.toprettyxml(indent="", newl="", encoding="")
+.. method:: Node.toprettyxml(indent="\t", newl="\n", encoding=None)
 
    Return a pretty-printed version of the document. *indent* specifies the
    indentation string and defaults to a tabulator; *newl* specifies the string