title: Wicked pdf not rendering header/footer
body: <p>I am using <a href="https://github.com/mileszs/wicked_pdf" rel="noreferrer">wicked_pdf</a> for generating <code>pdf</code> from <code>html</code> on my rails project. It is rendering <code>template</code> but I could not manage to print <code>header/footer</code> sections. Below is my code that print only <code>template</code> section</p>
  
  <pre><code>render pdf: "pdf_name",
                 layout: 'application',
                 template: 'reports/show',
                 formats: [:html],
                 margin: { top: 10, bottom: 10, left: 10, right: 10 },
                 disable_javascript: true,
                 show_as_html: params[:debug],
                 header: {
                   html: { template: 'shared/header' },
                   spacing: 10
                 },
                 footer: {
                   html: { template: 'shared/footer' },
                   spacing: 30,
                   line: true
                 }
  </code></pre>
  
  <p>If I try to use <code>WickedPdf.new.pdf_from_string render_to_string</code> it show <code>Failed to load PDF document</code> error even simple <code>WickedPdf.new.pdf_from_string('&lt;html&gt;&lt;body&gt;&lt;h1&gt;Hello There!&lt;/h1&gt;&lt;/body&gt;&lt;/html&gt;')</code> does not work. </p>
  
  <p>I have tried to use <code>render_to_string_with_wicked_pdf, render_with_wicked_pdf</code> but did not success. My Rails version is <code>3.2.19</code>, <code>wicked_pdf</code> gem version is <code>1.1.0</code> and <code>wkhtmltopdf</code> version is <code>wkhtmltopdf-0.13.0-alpha-7b36694_linux-trusty-amd64.deb</code>. I also tried to use <code>wkhtmltopdf</code> version <code>0.12.0</code>.</p>
  
  <p>My questions are</p>
  
  <ol>
  <li>Why my above implementation does not work?</li>
  <li>Why <code>pdf_from_string</code> does not work?</li>
  </ol>
  
  <p>Any kind of help is appreciated. Thanks.</p>