Upgrade Reactor to 2020.0.18

Closes gh-2060

Author: eleftherias

gradle/dependency-management.gradle

@@ -1,6 +1,6 @@
 dependencyManagement {
 	imports {
-		mavenBom 'io.projectreactor:reactor-bom:2020.0.16'
+		mavenBom 'io.projectreactor:reactor-bom:2020.0.18'
 		mavenBom 'org.junit:junit-bom:5.7.2'
 		mavenBom 'org.springframework:spring-framework-bom:5.3.16'
 		mavenBom 'org.springframework.data:spring-data-bom:2021.0.9'