Update child_process.markdown, spelling

'the' to 'then'

Reviewed-By: James M Snell <jasnell@gmail.com>
PR-URL: https://github.com/joyent/node/pull/25591

doc/api/child_process.markdown

@@ -274,7 +274,7 @@ Here is an example of sending a server:
       child.send('server', server);
     });
 
-And the child would the receive the server object as:
+And the child would then receive the server object as:
 
     process.on('message', function(m, server) {
       if (m === 'server') {