Remove unused dependency to slf4j-ext due to security issue

see for details:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-8088

Author: Thorbias

pom.xml

@@ -13,8 +13,8 @@
   ~ See the License for the specific language governing permissions and
   ~ limitations under the License.
   -->
-<project 
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
+<project
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="http://maven.apache.org/POM/4.0.0" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <groupId>com.networknt</groupId>
@@ -81,11 +81,6 @@
             <artifactId>slf4j-api</artifactId>
             <version>${version.slf4j}</version>
         </dependency>
-        <dependency>
-            <groupId>org.slf4j</groupId>
-            <artifactId>slf4j-ext</artifactId>
-            <version>${version.slf4j}</version>
-        </dependency>
         <dependency>
             <groupId>org.apache.commons</groupId>
             <artifactId>commons-lang3</artifactId>