move stdout from devDependencies to dependencies

When installing dat as a dependency in another package (^v5.0.1), I got this error:

```
Error: Cannot find module 'stdout'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at Object.<anonymous> (/Users/sethvincent/workspace/flatsheet/experiments/multi-dat/node_modules/dat/lib/transformations.js:9:14)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.require (module.js:364:17)
```

Moving stdout to the dependencies field in package.json fixes it.