{
  "name": "reg-suit-interface",
  "version": "0.7.0",
  "description": "",
  "typings": "lib/index.d.ts",
  "scripts": {
    "test": "echo T.B.D.",
    "prepublish": "tsc -p src/tsconfig.build.json"
  },
  "keywords": [
    "reg"
  ],
  "author": {
    "name": "Quramy",
    "email": "yosuke.kurami@gmail.com"
  },
  "repository": "git+https://github.com/reg-viz/reg-suit.git",
  "license": "MIT",
  "devDependencies": {
    "@types/inquirer": "^0.0.35",
    "typescript": "~2.5.3"
  }
}

{
  "name": "reg-suit-interface",
  "version": "0.7.0",
  "description": "",
  "typings": "lib/index.d.ts",
  "scripts": {
    "test": "echo T.B.D.",
    "prepublish": "tsc -p src/tsconfig.build.json"
  },
  "keywords": [
    "reg"
  ],
  "author": {
    "name": "Quramy",
    "email": "yosuke.kurami@gmail.com"
  },
  "repository": "git+https://github.com/reg-viz/reg-suit.git",
  "license": "MIT",
  "dependencies": {
    "@types/inquirer": "^0.0.35"
  },
  "devDependencies": {
    "typescript": "~2.5.3"
  }
}

Make `@types/inquirer` a regular dependency
Make `@types/inquirer` a regular dependency

`reg-suit-interface` exports `lib/plugin.d.ts`, which references `inquirer`. Since `inquirer` is a dev dependency, though, TypeScript chokes on the reference, because `@types/inquirer` isn't installed in libraries that depend on `reg-suit-interface`.