package.json has key `devDendencies`

```
  "devDendencies": {
    "babel-cli": "^6.8.0",
    "babel-plugin-syntax-flow": "^6.8.0",
    "babel-plugin-transform-flow-strip-types": "^6.8.0",
    "babel-preset-react-native": "^1.7.0",
    "clamp": "^1.0.1",
    "fbjs": "^0.8.1",
    "react-addons-pure-render-mixin": "^15.1.0"
  },
  "devDependencies": {},
```

I'm assuming that we want devDependencies, not devDendencies.
