log4j version upgrade for CVE-2021-44228 (#726)

Fixes #725

Signed-off-by: Yakir Gibraltar <yakir.g@taboola.com>

Co-authored-by: Yakir Gibraltar <yakir.g@taboola.com>

Author: yakirgb

simpleclient_log4j2/pom.xml

@@ -41,7 +41,7 @@
         <dependency>
             <groupId>org.apache.logging.log4j</groupId>
             <artifactId>log4j-core</artifactId>
-            <version>2.1</version>
+            <version>2.15.0</version>
         </dependency>
 
         <dependency>