Update versions; prepare for release

Author: garyrussell

build.gradle

@@ -83,9 +83,9 @@ subprojects { subproject ->
 		log4jVersion = '2.11.2'
 		mockitoVersion = '2.26.0'
 		scalaVersion = '2.11'
-		springDataCommonsVersion = '2.1.17.RELEASE'
+		springDataCommonsVersion = '2.1.18.RELEASE'
 		springRetryVersion = '1.2.5.RELEASE'
-		springVersion = '5.1.15.RELEASE'
+		springVersion = '5.1.16.RELEASE'
 
 		idPrefix = 'kafka'