MEECROWAVE-293 upgrade to Johnzon-1.2.12

Johnzon-1.2.11 had a bug regarding JsonbSerializers.
diff --git a/pom.xml b/pom.xml
index a84e58b..66d2e93 100644
--- a/pom.xml
+++ b/pom.xml
@@ -54,7 +54,7 @@
     <tomcat.version>9.0.46</tomcat.version>
     <openwebbeans.version>2.0.22</openwebbeans.version>
     <cxf.version>3.4.3</cxf.version>
-    <johnzon.version>1.2.11</johnzon.version>
+    <johnzon.version>1.2.12</johnzon.version>
     <log4j2.version>2.14.1</log4j2.version>
     <deltaspike.version>1.8.2</deltaspike.version>
     <jaxb.version>2.2.11</jaxb.version>