fix trailing whitespace

Doc/library/xml.etree.elementtree.rst

@@ -767,7 +767,7 @@ XMLParser Objects
    :class:`Element` structure builder for XML source data, based on the expat
    parser.  *html* are predefined HTML entities.  This flag is not supported by
    the current implementation.  *target* is the target object.  If omitted, the
-   builder uses an instance of the standard :class:`TreeBuilder` class. 
+   builder uses an instance of the standard :class:`TreeBuilder` class.
    *encoding* [1]_ is optional.  If given, the value overrides the encoding
    specified in the XML file.