fix: pom.xml to reduce vulnerabilities (#15)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-72448
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-72449
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-72451

pom.xml

@@ -33,7 +33,7 @@
             <roles>
                 <role>developer</role>
             </roles>
-            <email />
+            <email/>
         </developer>
     </developers>
 
@@ -58,7 +58,7 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <java.version>1.8</java.version>
         <kpl.version>0.12.9</kpl.version>
-        <jackson.version>2.9.7</jackson.version>
+        <jackson.version>2.9.8</jackson.version>
         <postgres.version>42.2.2</postgres.version>
         <junit.version>4.11</junit.version>
         <powermock.version>1.7.3</powermock.version>