Modified code to close the app after checking API >= 21

If API >= 21, Closed the app when press back button from App passcode screen

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

@@ -23,6 +23,7 @@
 package com.owncloud.android.ui.activity;
 
 import android.content.Intent;
+import android.os.Build;
 import android.os.Bundle;
 import android.os.SystemClock;
 import android.text.Editable;
@@ -365,9 +366,9 @@ 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())){
+            if(ACTION_CHECK.equals(getIntent().getAction()) && Build.VERSION.SDK_INT>=21){
                 moveTaskToBack(true);
-                finish();
+                finishAndRemoveTask();
             }else if (ACTION_REQUEST_WITH_RESULT.equals(getIntent().getAction()) ||
                 ACTION_CHECK_WITH_RESULT.equals(getIntent().getAction())) {
                 finish();