title: Get relative path of the file for tasks in vscode
body: <p>I have a task defined in vscode's tasks.json file as following</p>
  
  <pre><code>{
      "version": "0.1.0",
      "tasks": [
          {
              "command": "gulp",
              "taskName": "eslint_task",
              "args": [
                  "eslint",
                  "--file",
                  "${file}"
              ],
              "echoCommand": true
          }
      ]
  }
  </code></pre>
  
  <p>The <code>${file}</code> is providing me the absolute path (starting from <code>/Volumes</code> in macOS) of the file on which I run this command. Is there any way I can get the relative path (Path starting from the workspace folder) of the same file instead? </p>
  
  <p>I already checked the <a href="https://code.visualstudio.com/docs/editor/tasks" rel="noreferrer">official documentation for tasks</a>, but couldn't find any list of arguments there.</p>