Update checkstyle dependency.

Since we now use JDK 11

build.gradle

@@ -30,7 +30,7 @@ allprojects {
         nanojsonVersion = "1d9e1aea9049fc9f85e68b43ba39fe7be1c1f751"
         spotbugsVersion = "4.7.3"
         junitVersion = "5.9.1"
-        checkstyleVersion = "9.3" // do not use latest version (10.0) as it requires compile JDK 11
+        checkstyleVersion = "10.4"
     }
 }