Make ConfigHolder modifier order comply with java language spec.

Author: phipag

powertools-serialization/src/main/java/software/amazon/lambda/powertools/utilities/JsonConfig.java

@@ -123,7 +123,7 @@ public <T extends BaseFunction> void addFunction(T function) {
         jmesPath = new JacksonRuntime(updatedConfig, getObjectMapper());
     }
 
-    private final static class ConfigHolder {
+    private static final class ConfigHolder {
         private static final JsonConfig instance = new JsonConfig();
     }
 }