Bump slf4j dependency version to 1.7.30.

Author: heuermh

pom.xml

@@ -72,7 +72,7 @@
     <scala-guice.version>4.2.6</scala-guice.version>
     <scala.version>2.11.12</scala.version>
     <scala.version.prefix>2.11</scala.version.prefix>
-    <slf4j.version>1.7.25</slf4j.version>
+    <slf4j.version>1.7.30</slf4j.version>
     <spark.version>2.4.5</spark.version>
   </properties>
   <build>