title: Cannot convert value of type 'String' to expected argument type 'URLSession'
body: <p>I use Alamofire 4.0, Swift 4.2 and Xcode 10.2 to request Http Api
  I have url constant:</p>
  
  <pre><code>let weatherUrl = "http://api.openweathermap.org/data/2.5/weather"
  </code></pre>
  
  <p>And function:</p>
  
  <pre><code>func getWeatherData(url: String, parameters: [String : String])
      {
          Alamofire.Request(url, parameters: parameters).responseJSON
          {
                  response in
          }
  
  getWeatherData(url: weatherUrl, parameters: params)
  </code></pre>
  
  <p>And Xcode notify me:"Cannot convert value of type 'String' to expected argument type 'URLSession'".</p>
  
  <p><img src="https://i.stack.imgur.com/Q1Bqj.png" alt="Alamofire"></p>
  
  <p>What is the problem?</p>