title: jsreport-core: using header with phantom-pdf receipe
body: <p>I've a jsreport-core based app, the content template is renderd fine, but the header is not renderd. Here the the basic steps in my app:      </p>
  
  <pre><code>import jsreportCore from 'jsreport-core';
  import jsreportFsStore from 'jsreport-fs-store';
  import jsreportTemplates from 'jsreport-templates';
  import jsreportJsrender from 'jsreport-jsrender';
  import jsreportPhantomPdf from 'jsreport-phantom-pdf';
  import jsreportExpress from 'jsreport-express';
  
  // ...
  
  jsreport.use(new jsreportFsStore({dataDirectory: "data", syncModifications: true}));
  jsreport.use(new jsreportTemplates());
  jsreport.use(new jsreportJsrender);
  jsreport.use(new jsreportPhantomPdf());
  jsreport.use(new jsreportExpress({app : app}));
  
  // ...
  const jsreport = new jsreportCore({
     loadConfig: false,
     autoTempCleanup: true,
     connectionString: { 'name': 'fs' },
     tasks: { allowedModules: '*' }
  });
  
  // ...
  
  
  jsreport.render({ template : {name: "foo",engine: "jsrender",recipe:"phantom-pdf"},data : dataObj}).then((out) =&gt; {
        out.stream.pipe(res);
      }).catch((e) =&gt; {
        res.end(e.message);
      });
  </code></pre>
  
  <p>This is the template directory structure where the content templated is loaded from. (Same as from jsreport-studio).  </p>
  
  <pre><code>---- data
  ------ templates
  -------- foo
  ---------- content.html
  ---------- header.html
  </code></pre>