Upgrade rxjava2 2.2.18

Author: slandelle

pom.xml

@@ -458,7 +458,7 @@
     <activation.version>1.2.0</activation.version>
     <netty-reactive-streams.version>2.0.4</netty-reactive-streams.version>
     <rxjava.version>1.3.8</rxjava.version>
-    <rxjava2.version>2.2.12</rxjava2.version>
+    <rxjava2.version>2.2.18</rxjava2.version>
     <logback.version>1.2.3</logback.version>
     <testng.version>6.13.1</testng.version>
     <jetty.version>9.4.18.v20190429</jetty.version>