Upgrade to Reactor Californium-SR19

Closes spring-projectsgh-25211

build.gradle

@@ -38,7 +38,7 @@ ext {
 	kotlinVersion        = "1.2.71"
 	log4jVersion         = "2.11.2"
 	nettyVersion         = "4.1.50.Final"
-	reactorVersion       = "Californium-SR18"
+	reactorVersion       = "Californium-SR19"
 	rxjavaVersion        = "1.3.8"
 	rxjavaAdapterVersion = "1.2.1"
 	rxjava2Version       = "2.2.19"