code: function insertScript (url) {
    const script = document.createElement('script')
  
    script.async = true
    script.src = url
  
    document.head.appendChild(script)
  
    return script
  }
docs: const LATEST_MIP_VERSION = '2' 
  Inserts a script element in `<head>` with specified url. Returns that script element.
  
  @param {string} url of script.
  @returns {!HTMLScriptElement}
  @private