Remove log4j-core dependency (#260)

diff --git a/pom.xml b/pom.xml
index fadbef3..005d85f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -93,10 +93,6 @@
     </dependency>
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
-      <artifactId>log4j-core</artifactId>
-    </dependency>
-    <dependency>
-      <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-slf4j2-impl</artifactId>
     </dependency>
     <dependency>