title: Using zsh when run task in vscode
body: <p>What I want to achieve is using zsh in "output" pane whenever I run a Task in VSCode, but it keep using <code>/bin/sh</code> instead. 
  The "Terminal" pane is using zsh correctly though.</p>
  
  <p>Here's my configurations:</p>
  
  <pre><code>➜  ~ echo $SHELL
  /bin/zsh
  ➜  ~ which zsh
  /bin/zsh
  </code></pre>
  
  <p>tasks.json</p>
  
  <pre><code>{
    "version": "0.1.0",
    "command": "echo Im $0",
    "suppressTaskName": true,
    "isShellCommand": {
      "executable": "/bin/zsh"
    },
    "showOutput": "always",
    "tasks": [
      {
        "taskName": "Test",
        "args": ["test"]
      }
    ]
  }
  </code></pre>
  
  <p>And the output when I run the Task is:
  <code>Im /bin/sh</code></p>