Use fetched template in usage example

Blooper introduced when making the usage examples in README.md
more modern a couple of days ago, where the example fetching the
mustache template over HTTP, didn't in fact use the fetched template.

Author: phillipj

README.md

@@ -92,7 +92,6 @@ function renderHello() {
   fetch('template.mustache')
     .then((response) => response.text())
     .then((template) => {
-      var template = document.getElementById('template').innerHTML;
       var rendered = Mustache.render(template, { name: 'Luke' });
       document.getElementById('target').innerHTML = rendered;    
     });