title: jspdf.addHTML throwing an error
body: <p>Using jsPDF in angular 2, I am running this code on a button click:</p>
  
  <pre><code>generatePDF(){
      const options = {'pagesplit': true}
      this.pdf.addHTML(this.id.nativeElement, 10, 10, options, function(){
        this.pdf.save('test.pdf')
      }); 
  }
  </code></pre>
  
  <p>onClick the generatePDF function is called and throws this error without generating the pdf:
  <strong>html2canvas: onrendered option is deprecated, html2canvas returns a Promise with the canvas as the value</strong>
  I have checked the official documentation of <a href="http://rawgit.com/MrRio/jsPDF/master/docs/global.html#addHTML" rel="nofollow noreferrer">jsPDF</a>, it does say it is deprecated.</p>
  
  <p>I would appreciate some help on this. Thanks!</p>