Upgrade Reactor to 2020.0.15

Closes gh-2009

Author: eleftherias

gradle/dependency-management.gradle

@@ -1,6 +1,6 @@
 dependencyManagement {
 	imports {
-		mavenBom 'io.projectreactor:reactor-bom:2020.0.12'
+		mavenBom 'io.projectreactor:reactor-bom:2020.0.15'
 		mavenBom 'com.fasterxml.jackson:jackson-bom:2.13.1'
 		mavenBom 'org.junit:junit-bom:5.8.1'
 		mavenBom 'org.springframework:spring-framework-bom:6.0.0-M2'