doc: update tense in child_process.markdown

per: https://github.com/joyent/node/pull/25826

originally submitted by: @ClimbsRocks

Reviewed By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
PR-URL: https://github.com/nodejs/node/pull/2378

doc/api/child_process.markdown

@@ -88,7 +88,7 @@ and the `.connected` property is false.
 * `message` {Object} a parsed JSON object or primitive value
 * `sendHandle` {Handle object} a Socket or Server object
 
-Messages send by `.send(message, [sendHandle])` are obtained using the
+Messages sent by `.send(message, [sendHandle])` are obtained using the
 `message` event.
 
 ### child.stdin