message: build: use rimraf and mkdirp for prebuild script
diff: "lint": "eslint src test",
  "pretest": "npm run build",
  "test": "mocha",
  - "prebuild": "rm -rf dist && mkdir -p dist && npm run flow && npm run lint",
  + "prebuild": "rimraf dist && mkdirp dist && npm run flow && npm run lint",
  "build": "rollup -c",
  "prepublish": "npm run build",
  "semantic-release": "semantic-release pre && npm publish && semantic-release post"
  "eslint-plugin-decaffeinate": "file:eslint-rules",
  "eslint-plugin-flow-vars": "^0.5.0",
  "flow-bin": "^0.37.0",
  + "mkdirp": "^0.5.1",
  "mocha": "^3.0.0",
  "mversion": "^1.10.1",
  + "rimraf": "^2.5.4",
  "rollup": "^0.40.0",
  "rollup-plugin-babel": "^2.6.1",
  "rollup-plugin-json": "^2.0.1",
  