Doesn't pass `stream-spec` standardized test

Nobody has claimed this yet.

@dominictarr's [stream-spec](https://github.com/dominictarr/stream-spec) for testing stream implementations

``` js
var WebWorkify = require('webworkify')
var WorkerStream = require('../index.js')
var spec = require('stream-spec')

var worker = WebWorkify(require('./ps-loopback-worker.js'))
var workerStream = WorkerStream(worker)

spec(workerStream)
.through({strict: true})
.validateOnExit()
```

results in

```
Uncaught AssertionError: stream *must* have pause
```

I'm sure there are other assertions once you get past this one.

Run the stream-spec example from the issue against index.js, beginning with WorkerStream and the ps-loopback-worker.js fixture. Use the reported missing pause assertion as the first checkpoint; done means the worker stream passes the chained through({strict: true}).validateOnExit() checks.

Written by the indexing model from the issue text.