Upgrade to Californium snapshots

Towards Californium SR2 to confirm fix for SPR-17306.

build.gradle

@@ -38,7 +38,7 @@ ext {
 	kotlinVersion        = "1.2.71"
 	log4jVersion         = "2.11.1"
 	nettyVersion         = "4.1.30.Final"
-	reactorVersion       = "Californium-SR1"
+	reactorVersion       = "Californium-BUILD-SNAPSHOT"
 	rxjavaVersion        = "1.3.8"
 	rxjavaAdapterVersion = "1.2.1"
 	rxjava2Version       = "2.2.3"
@@ -148,6 +148,7 @@ configure(allprojects) { project ->
 
 	repositories {
 		maven { url "https://repo.spring.io/libs-release" }
+		maven { url "https://repo.spring.io/snapshot" } // Californium snapshots
 	}
 
 	dependencies {

spring-webflux/src/test/java/org/springframework/web/reactive/socket/WebSocketIntegrationTests.java

@@ -197,7 +197,10 @@ public class WebSocketIntegrationTests extends AbstractWebSocketIntegrationTests
 
 		@Override
 		public Mono<Void> handle(WebSocketSession session) {
-			return Flux.never().mergeWith(session.close(CloseStatus.GOING_AWAY)).then();
+			return session.send(Flux
+					.error(new Throwable())
+					.onErrorResume(ex -> session.close(CloseStatus.GOING_AWAY)) // SPR-17306 (nested close)
+					.cast(WebSocketMessage.class));
 		}
 	}