Bump OUTDATED_SERVER_VERSION to 19

Signed-off-by: Álvaro Brey Vilas <alvaro.brey@nextcloud.com>

src/main/java/com/owncloud/android/MainApp.java

@@ -120,7 +120,7 @@ import static com.owncloud.android.ui.activity.ContactsPreferenceActivity.PREFER
  */
 public class MainApp extends MultiDexApplication implements HasAndroidInjector {
 
-    public static final OwnCloudVersion OUTDATED_SERVER_VERSION = OwnCloudVersion.nextcloud_18;
+    public static final OwnCloudVersion OUTDATED_SERVER_VERSION = OwnCloudVersion.nextcloud_19;
     public static final OwnCloudVersion MINIMUM_SUPPORTED_SERVER_VERSION = OwnCloudVersion.nextcloud_16;
 
     private static final String TAG = MainApp.class.getSimpleName();