use method expression lambdas to further shorten the code

src/main/java/com/owncloud/android/utils/FileSortOrderByDate.java

@@ -47,10 +47,8 @@ public class FileSortOrderByDate extends FileSortOrder {
     public List<OCFile> sortCloudFiles(List<OCFile> files) {
         final int multiplier = mAscending ? 1 : -1;
 
-        Collections.sort(files, (o1, o2) -> {
-                Long obj1 = o1.getModificationTimestamp();
-                return multiplier * obj1.compareTo(o2.getModificationTimestamp());
-        });
+        Collections.sort(files, (o1, o2) ->
+                multiplier * Long.compare(o1.getModificationTimestamp(), o2.getModificationTimestamp()));
 
         return super.sortCloudFiles(files);
     }
@@ -64,10 +62,8 @@ public class FileSortOrderByDate extends FileSortOrder {
     public List<File> sortLocalFiles(List<File> files) {
         final int multiplier = mAscending ? 1 : -1;
 
-        Collections.sort(files, (o1, o2) -> {
-            Long obj1 = o1.lastModified();
-            return multiplier * obj1.compareTo(o2.lastModified());
-        });
+        Collections.sort(files, (o1, o2) ->
+            multiplier * Long.compare(o1.lastModified(),o2.lastModified()));
 
         return files;
     }