Upgrade to Mongo Driver Reactivestreams 1.6.0

Closes gh-10334

spring-boot-dependencies/pom.xml

@@ -135,7 +135,7 @@
 		<micrometer.version>1.0.0-rc.1</micrometer.version>
 		<mssql-jdbc.version>6.2.1.jre8</mssql-jdbc.version>
 		<mockito.version>2.9.0</mockito.version>
-		<mongo-driver-reactivestreams.version>1.5.0</mongo-driver-reactivestreams.version>
+		<mongo-driver-reactivestreams.version>1.6.0</mongo-driver-reactivestreams.version>
 		<mongodb.version>3.5.0</mongodb.version>
 		<mysql.version>5.1.44</mysql.version>
 		<narayana.version>5.6.4.Final</narayana.version>