message: Fix background property in problemMatcher
diff: {
  "label": "compile",
  "type": "npm",
  - "script": "compile",
  + "script": "compile"
  },
  {
  "label": "watch:compile",
  "isDefault": true
  },
  "isBackground": true,
  - "problemMatcher": [{
  + "problemMatcher": [
  + {
  "applyTo": "allDocuments",
  "owner": "typescript",
  "source": "webpack",
  "regexp": "\\s*TS\\d+:\\s*(.*)",
  "message": 1
  }
  - ]
  - }],
  + ],
  "background": {
  "activeOnStart": true,
  "beginsPattern": {
  }
  ]
  }
  + ]
  +}
  