message: add acorn to devDependencies
diff: "@types/ws": "^4.0.2",
  "@typescript-eslint/eslint-plugin": "^2.1.0",
  "@typescript-eslint/parser": "^2.1.0",
  + "acorn": "^6.2.1",
  "eslint": "^6.3.0",
  "husky": "^3.0.2",
  "textmate-bailout": "^1.1.0",
  