Send a "ARTICLE" --> Send an "ARTICLE"

Usage error noted by Grant Griffin <grant.griffin@iowegian.com>.

Doc/lib/libnntplib.tex

@@ -203,7 +203,7 @@ Send a \samp{BODY} command, where \var{id} has the same meaning as for
 \end{methoddesc}
 
 \begin{methoddesc}{article}{id}
-Send a \samp{ARTICLE} command, where \var{id} has the same meaning as
+Send an \samp{ARTICLE} command, where \var{id} has the same meaning as
 for \method{stat()}.  Return as for \method{head()}.
 \end{methoddesc}