Upgrade to RxJava 1.3.1

Issue: SPR-15497

Author: jhoeller

build.gradle

@@ -60,7 +60,7 @@ configure(allprojects) { project ->
 	ext.nettyVersion         = "4.1.15.Final"
 	ext.okhttp3Version       = "3.9.0"
 	ext.reactorVersion       = "Bismuth-M4"
-	ext.rxjavaVersion        = '1.3.0'
+	ext.rxjavaVersion        = '1.3.1'
 	ext.rxjavaAdapterVersion = '1.2.1'
 	ext.rxjava2Version       = '2.1.3'
 	ext.slf4jVersion         = "1.7.25"