bpo-26730: Fix SpooledTemporaryFile data corruption (GH-17400)

SpooledTemporaryFile.rollback() might cause data corruption
when it is in text mode.

Co-Authored-By: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Doc/library/tempfile.rst b/Doc/library/tempfile.rst
index fff7a7a..a59817c 100644
--- a/Doc/library/tempfile.rst
+++ b/Doc/library/tempfile.rst
@@ -105,8 +105,8 @@
    causes the file to roll over to an on-disk file regardless of its size.
 
    The returned object is a file-like object whose :attr:`_file` attribute
-   is either an :class:`io.BytesIO` or :class:`io.StringIO` object (depending on
-   whether binary or text *mode* was specified) or a true file
+   is either an :class:`io.BytesIO` or :class:`io.TextIOWrapper` object
+   (depending on whether binary or text *mode* was specified) or a true file
    object, depending on whether :func:`rollover` has been called.  This
    file-like object can be used in a :keyword:`with` statement, just like
    a normal file.