Upgrade to Rxjava2 2.2.20

Closes gh-23848

Author: wilkinsona

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -179,7 +179,7 @@
 		<rsocket.version>1.0.2</rsocket.version>
 		<rxjava.version>1.3.8</rxjava.version>
 		<rxjava-adapter.version>1.2.1</rxjava-adapter.version>
-		<rxjava2.version>2.2.19</rxjava2.version>
+		<rxjava2.version>2.2.20</rxjava2.version>
 		<selenium.version>3.141.59</selenium.version>
 		<selenium-htmlunit.version>2.36.0</selenium-htmlunit.version>
 		<sendgrid.version>4.4.8</sendgrid.version>