Update Netty-socketio Maven dependency

Netty-socketio 1.7.3 fixes memory leaks.

pom.xml

@@ -256,7 +256,7 @@
 		<dependency>
 			<groupId>com.corundumstudio.socketio</groupId>
 			<artifactId>netty-socketio</artifactId>
-			<version>1.7.2</version>
+			<version>1.7.3</version>
 		</dependency>
 		<dependency>
 			<groupId>javax.inject</groupId>