data: Added private constructor for the Injection utility class.

Utility classes, which are collections of static members, are not meant to be instantiated. Even abstract utility classes, which can be extended, should not have public constructors.

Java adds an implicit public constructor to every class which does not define at least one explicitly. Hence, at least one non-public constructor should be defined.

src/main/java/com/owncloud/android/ui/activities/data/Injection.java

@@ -27,6 +27,10 @@ import com.owncloud.android.ui.activities.data.files.FilesServiceApiImpl;
 
 public class Injection {
 
+    private Injection () {
+        // Required empty constructor
+    }
+
     public static ActivitiesRepository provideActivitiesRepository() {
         return ActivityRepositories.getRepository(new ActivitiesServiceApiImpl());
     }