replaced "21" with "Build.VERSION_CODES.LOLLIPOP"

src/main/java/com/owncloud/android/ui/activity/PassCodeActivity.java

@@ -366,7 +366,7 @@ public class PassCodeActivity extends AppCompatActivity implements Injectable {
     @Override
     public boolean onKeyDown(int keyCode, KeyEvent event){
         if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount()== 0){
-            if(ACTION_CHECK.equals(getIntent().getAction()) && Build.VERSION.SDK_INT>=21){
+            if(ACTION_CHECK.equals(getIntent().getAction()) && Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP){
                 moveTaskToBack(true);
                 finishAndRemoveTask();
             }else if (ACTION_REQUEST_WITH_RESULT.equals(getIntent().getAction()) ||