Upgrade to RxJava 2.1

Issue: SPR-15497

Author: jhoeller

build.gradle

@@ -84,7 +84,7 @@ configure(allprojects) { project ->
 	ext.romeVersion            = "1.7.2"
 	ext.rxjavaVersion          = '1.2.10'
 	ext.rxjavaAdapterVersion   = '1.2.1'
-	ext.rxjava2Version         = '2.0.9'
+	ext.rxjava2Version         = '2.1.0'
 	ext.rxnettyVersion         = '0.5.2'
 	ext.servletVersion         = "3.1.0"
 	ext.slf4jVersion           = "1.7.25"