Fix minor cut-and-paste typo.

Doc/lib/email.tex

@@ -112,7 +112,7 @@ The \class{MIMEBase} class always adds a \mailheader{Content-Type} header
 
 A subclass of \class{MIMEBase}, the \class{MIMEAudio} class is used to
 create MIME message objects of major type \mimetype{audio}.
-\var{_audiodata} is a string containing the raw image data.  If this
+\var{_audiodata} is a string containing the raw audio data.  If this
 data can be decoded by the standard Python module \refmodule{sndhdr},
 then the subtype will be automatically included in the
 \mailheader{Content-Type} header.  Otherwise you can explicitly specify the