Prepare for 2.15.4 release

Author: cowtowncoder

pom.xml

@@ -49,7 +49,7 @@ of Jackson components maintained by FasterXML.com
   </scm>
 
   <properties>
-    <jackson.version>2.15.4-SNAPSHOT</jackson.version>
+    <jackson.version>2.15.4</jackson.version>
 
     <!-- 25-Sep-2019, tatu: With Jackson 2.x we will release full patch-level versions
            of annotations BUT they are all identical, content-wise.