"Trailer" header should mention "Content-MD5" trailer name in this example.

Fixes #2107

doc/api/http.markdown

@@ -358,7 +358,7 @@ Note that HTTP requires the `Trailer` header to be sent if you intend to
 emit trailers, with a list of the header fields in its value. E.g.,
 
     response.writeHead(200, { 'Content-Type': 'text/plain',
-                              'Trailer': 'TraceInfo' });
+                              'Trailer': 'Content-MD5' });
     response.write(fileData);
     response.addTrailers({'Content-MD5': "7895bf4b8828b55ceaf47747b4bca667"});
     response.end();