[jvm-packages] update checkstyle (#7335)

* [jvm-packages] update scalastyle

1. bump scalastyle-maven-plugin and maven-checkstyle-plugin to latest
2. remove unused imports

* fix code style check

jvm-packages/xgboost4j-gpu/src/main/java/ml/dmlc/xgboost4j/gpu/java/CudfUtils.java

@@ -90,9 +90,9 @@ class CudfUtils {
       shapeNode.add(shape);
       ArrayNode dataNode = objNode.putArray("data");
       dataNode.add(ptr)
-        .add(false);
+          .add(false);
       objNode.put("typestr", typeStr)
-        .put("version", 1);
+          .put("version", 1);
       return objNode;
     }
   }