message: Add peer dependencies. Fixes
diff: "license": "BSD-3-Clause",
  "main": "src/embed.js",
  "devDependencies": {
  - "browserify": "^14.0.0",
  + "browserify": "^14.1.0",
  "browserify-shim": "^3.8.13",
  "eslint": "^3.14.1",
  "uglify-js": "^2.7.5",
  - "vega": "3.0.0-beta.20",
  + "vega": "3.0.0-beta.22",
  "vega-lite": "2.0.0-alpha.1",
  + "watchify": "^3.9.0"
  + },
  + "dependencies": {
  "d3-selection": "^1.0.3",
  - "watchify": "^3.9.0",
  "vega-schema-url-parser": "^1.0.0-beta.2"
  },
  + "peerDependencies": {
  + "vega": "3",
  + "vega-lite": "2"
  + },
  "scripts": {
  "deploy": "npm run lint && scripts/deploy.sh",
  "lint": "eslint src/",
  