doc: fix typo in dgram docs

PR-URL: #50211
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Vinícius Lourenço Claro Cardoso <contact@viniciusl.com.br>

doc/api/dgram.md

@@ -902,7 +902,7 @@ to exclude the socket from the reference counting that keeps the Node.js
 process active, allowing the process to exit even if the socket is still
 listening.
 
-Calling `socket.unref()` multiple times will have no addition effect.
+Calling `socket.unref()` multiple times will have no additional effect.
 
 The `socket.unref()` method returns a reference to the socket so calls can be
 chained.