title: dojo build systems does not recognize es6 syntax
body: <p>I am working on a dojo project (1.11.x) and recently started using ES6(ES2015) syntax such as const, let and template literals. It worked fine until I build the project using dojo-util. I have errors like below</p>
  
  <pre><code>ERROR - Parse error. TypeError: redeclaration of const {variable name}
  ERROR - Parse error. illegal character
                       return `&lt;a href="/xxx/xxx/${a}"&gt;${b}&lt;/a&gt;`;
                              ^
  </code></pre>
  
  <p>Is there any way to make the build system recognize ES6 syntax or bypass the syntax checking?</p>