title: nightwatch selenium command "elements" returns error about first parameter, even when I pass in a css selector or xpath expression
body: <p>I'm using nightwatch with selenium for automation testing. I'm trying to use the selenium command 'elements' which takes a css selector or xpath as the first parameter, but keep getting the following error : </p>
  
  <p>Error while running elements command: Please provide any of the following using strings as the first parameter: class name, css selector, id, name, link text, partial link text, tag name or xpath</p>
  
  <p>My use is like this:</p>
  
  <pre><code>module.exports = {
      "My test" : function (browser) {
         ...  
         // want to get all the input elements from the document
         browser.elements('input','name', function(els){
         // of xpath like this
         browser.elements('//input','name', function(els){
         });
      }
  </code></pre>
  
  <p>}</p>
  
  <p>Any ideas why I'm getting this error? Thanks!</p>