Merge pull request #597 from InterestingLab/rickyhuo.fixbug.595

Fix #595

Author: garyelephant

waterdrop-core/src/main/scala/io/github/interestinglab/waterdrop/filter/Grok.scala

@@ -16,7 +16,7 @@ import scala.collection.JavaConverters._
 
 class Grok extends BaseFilter {
 
-  val grok = GrokLib.EMPTY
+  val grok = new GrokLib()
 
   var conf: Config = ConfigFactory.empty()