Upgrade to Reactor Californium M1

Issue: SPR-16386

build.gradle

@@ -40,7 +40,7 @@ ext {
 	kotlinVersion        = "1.2.51"
 	log4jVersion         = "2.11.0"
 	nettyVersion         = "4.1.27.Final"
-	reactorVersion       = "Californium-BUILD-SNAPSHOT"
+	reactorVersion       = "Californium-M1"
 	rxjavaVersion        = "1.3.8"
 	rxjavaAdapterVersion = "1.2.1"
 	rxjava2Version       = "2.1.17"
@@ -150,7 +150,7 @@ configure(allprojects) { project ->
 
 	repositories {
 		maven { url "https://repo.spring.io/libs-release" }
-		maven { url "https://repo.spring.io/snapshot" }  // for Reactor
+		maven { url "https://repo.spring.io/milestone" }  // for Reactor
 	}
 
 	dependencies {