Add undertow websockets dependency

spring-boot-samples/spring-boot-sample-websocket-undertow/pom.xml

@@ -34,6 +34,10 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-undertow</artifactId>
 		</dependency>
+		<dependency>
+			<groupId>io.undertow</groupId>
+			<artifactId>undertow-websockets-jsr</artifactId>
+		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-actuator</artifactId>