Upgrade to SLF4J 1.7.30 and Checkstyle 8.28

Author: jhoeller

build.gradle

@@ -42,7 +42,7 @@ ext {
 	rxjavaVersion        = "1.3.8"
 	rxjavaAdapterVersion = "1.2.1"
 	rxjava2Version       = "2.2.16"
-	slf4jVersion         = "1.7.28"	  // spring-jcl + consistent 3rd party deps
+	slf4jVersion         = "1.7.30"	  // spring-jcl + consistent 3rd party deps
 	tiles3Version        = "3.0.8"
 	tomcatVersion        = "9.0.30"
 	undertowVersion      = "2.0.29.Final"
@@ -142,7 +142,7 @@ configure(allprojects) { project ->
 	}
 
 	checkstyle {
-		toolVersion = "8.27"
+		toolVersion = "8.28"
 		configDir = rootProject.file("src/checkstyle")
 	}