Refactor: Make field final

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/database/FeatureCache.java

@@ -34,7 +34,7 @@ public class FeatureCache implements CityObjectCache{
 
     private final LoadingCache<GmlId, CityObject> cache;
     private final DatabaseHandler handler;
-    private AtomicInteger putsCounter = new AtomicInteger(0);
+    private final AtomicInteger putsCounter = new AtomicInteger(0);
     private boolean parsingFinished = false;
 
     FeatureCache() {