fix: pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-COMFASTERXMLJACKSONCORE-2326698

Author: snyk-bot

pom.xml

@@ -74,7 +74,7 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <buildNumber>${user.name}-${maven.build.timestamp}</buildNumber>
 
-        <jackson.version>2.12.5</jackson.version>
+        <jackson.version>2.12.6</jackson.version>
         <orgjson.version>20180130</orgjson.version>
         <gson.version>2.8.8</gson.version>