title: tasks.json exists but 'No task defined'
body: <p>I have a tasks.json open in VSCode. When I try to 'Run Task' I get 'No task to be run. Configure Tasks'.</p>
  
  <p>Trying to Configure Tasks I get 'Open tasks.json'. But tasks.json is already open in VSCode. Closing tasks.json and reopening it gives the same result.</p>
  
  <p>Help appreciated. tasks.json shown below.</p>
  
  <pre><code>{
    // See https://go.microsoft.com/fwlink/?LinkId=733558
    // for the documentation about the tasks.json format
    "version": "2.0.0",
     "label": "GnuCOBOL - Compile (single file)",
     "type": "shell",
     "options": {
      "env": {
          "PATH":"\\gnucobol3\\bin",
          "COB_CONFIG_DIR": "c:\\gnucobol3\\config",
          "COB_COPY_DIR": "c:\\gnucobol3\\copy",
          "COB_INCLUDE_PATH": "c:\\gnucobol3\\include",
          "COB_LIB_PATH": "c:\\gnucobol3\\lib",
         },
      "command": "cobc",
      "args": [
        "-x",
        "-std=mf",
        "-t${fileBasenameNoExtension}.LST",
        "${file}"
        ]
      },
  } 
  </code></pre>