Patch #993187: Make rstrip doc similar to lstrip.

Backported to 2.3.

Doc/lib/libstring.tex

@@ -271,7 +271,7 @@ removed.  If given and not \code{None}, \var{chars} must be a string;
 the characters in the string will be stripped from the end of the
 string this method is called on.
 \versionchanged[The \var{chars} parameter was added.  The \var{chars}
-parameter cannot be passed in 2.2 versions]{2.2.3}
+parameter cannot be passed in earlier 2.2 versions]{2.2.3}
 \end{funcdesc}
 
 \begin{funcdesc}{strip}{s\optional{, chars}}