Update article.md

Author: Violet-Bora-Lee

5-network/10-long-polling/article.md

@@ -1,6 +1,6 @@
 # Long polling
 
-Long polling is the simplest way of having persistent connection with server, that doesn't use any specific protocol like WebSocket or Server Side Events.
+Long polling is the simplest way of having persistent connection with server, that doesn't use any specific protocol like WebSocket or Server Sent Events.
 
 Being very easy to implement, it's also good enough in a lot of cases.