ui:preview Replace deprecated setOnPageChangeListener() method with addOnPageChangeListener().

src/main/java/com/owncloud/android/ui/preview/PreviewImageActivity.java

@@ -154,7 +154,7 @@ public class PreviewImageActivity extends FileActivity implements
         position = (position >= 0) ? position : 0;
 
         mViewPager.setAdapter(mPreviewImagePagerAdapter);
-        mViewPager.setOnPageChangeListener(this);
+        mViewPager.addOnPageChangeListener(this);
         mViewPager.setCurrentItem(position);
 
         if (position == 0 && !getFile().isDown()) {