title: Dragula :revert drop in ng2-dragula
body: <p>i have an <code>angular2</code> app with <code>typescript</code>. I am using <a href="https://github.com/bevacqua/dragula" rel="noreferrer">ng2-dragula</a> to make a drag and drop application.</p>
  
  <p>I am requiered to, <strong>check a condition, and revert the drag if the condition is false</strong>, and I know from <a href="https://github.com/bevacqua/dragula" rel="noreferrer">here</a>, that <code>revertOnSpill</code> that <code>revertOnSpill:true</code> can put the element back to its first place. </p>
  
  <p>But, <strong>I don't know how is it possible in</strong> <code>ng2-dragula</code>.
   i implimented it in the <code>onDrop</code>. here is the code</p>
  
  <pre><code> constructor() {
  
                dragulaService.drop.subscribe((value) =&gt; {
                    this.onDrop(value.slice(1));
                });
  
                  dragulaService.setOptions('second-bag', {
                    removeOnSpill: true
                });
   }
  
  private onDrop(args) {
     bla
     bla
     bla
     if(err.status=="404")                                                               
            this.dragulaService.removeModel;
           // this.dragulaService.cancel; also tried but did not work   
  }
  </code></pre>
  
  <p>and here is the html code:</p>
  
  <pre><code>&lt;div   id="toPlay" class="playBox roundedBox" [dragula]="'second-bag'"&gt;
      &lt;img class="w3-animate-top" [src]="sax_path" alt="sax" id="saxsophone"/&gt;
      &lt;img class="w3-animate-top" [src]="drum_path" alt="drum" id="drum"/&gt; 
  &lt;/div&gt;
  &lt;div   id="scene"  [dragula]="'second-bag'"&gt;
  
  &lt;/div&gt; 
  </code></pre>
  
  <p>Package.json is:</p>
  
  <pre><code> "dependencies": {
      "dragula": "^3.7.2"
    },
    "peerDependencies": {
      "@angular/common": "^2.0.0",
      "@angular/core": "^2.0.0",
      "@angular/compiler": "^2.0.0",
      "@angular/forms": "^2.0.0"
    },
    "devDependencies": {
      "angular-cli": "1.0.0-beta.22-1",
      "typescript": "2.0.10"
    }
  </code></pre>
  
  <p>the problem is, <strong>i don't know how to cancel the drop?</strong></p>