fix two minor issues by SonarLint

src/main/java/org/heigit/ohsome/oshdb/examples/analyses/DistinctContributors.java

@@ -6,6 +6,7 @@ import org.heigit.ohsome.oshdb.OSHDBBoundingBox;
 import org.heigit.ohsome.oshdb.OSHDBTimestamp;
 import org.heigit.ohsome.oshdb.api.db.OSHDBH2;
 import org.heigit.ohsome.oshdb.api.mapreducer.OSMContributionView;
+import org.heigit.ohsome.oshdb.util.mappable.OSMContribution;
 import org.heigit.ohsome.oshdb.util.time.OSHDBTimestamps.Interval;
 import org.heigit.ohsome.oshdb.util.time.TimestampFormatter;
 
@@ -27,7 +28,7 @@ public class DistinctContributors {
           .areaOfInterest(new OSHDBBoundingBox(71.45, -1.16, 74.7, 7.47)) // maldives
           .timestamps("2007-01-01", "2017-12-01", Interval.MONTHLY)
           .filter("type:way and highway=*")
-          .map(k -> k.getContributorUserId())
+          .map(OSMContribution::getContributorUserId)
           .aggregateByTimestamp()
           .countUniq();
     }

src/main/java/org/heigit/ohsome/oshdb/tutorial/TutorialChart.java

@@ -43,10 +43,9 @@ public class TutorialChart extends ApplicationFrame {
         .iterator();
     while (it.hasNext()) {
       Map.Entry<OSHDBTimestamp, Map<ContributionType, Integer>> ff = it.next();
-      Arrays.asList(ContributionType.values()).forEach((ContributionType contribType) -> {
-        a.addValue(ff.getValue().get(contribType), contribType, ff
-            .getKey());
-      });
+      Arrays.asList(ContributionType.values()).forEach((ContributionType contribType) -> a
+          .addValue(ff.getValue().get(contribType), contribType, ff
+              .getKey()));
     }
     return a;
   }