Bump johnzon-mapper from 1.2.19 to 1.2.21

Bumps johnzon-mapper from 1.2.19 to 1.2.21.

---
updated-dependencies:
- dependency-name: org.apache.johnzon:johnzon-mapper
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/pom.xml b/pom.xml
index bf7fc2d..bfbe66f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -59,7 +59,7 @@
         <geronimo.jaxrs.version>1.1</geronimo.jaxrs.version>
         <geronimo.json.version>1.5</geronimo.json.version>
         <hamcrest.version>2.2</hamcrest.version>
-        <johnzon.version>1.2.19</johnzon.version>
+        <johnzon.version>1.2.21</johnzon.version>
         <jackson.version>2.14.1</jackson.version>
         <jaxb.version>2.3.3</jaxb.version>
         <jaxws.version>2.3.3</jaxws.version>