fix; command field in tap output not valid

Currently this fails:

```
not ok 1 test/settings/settings-test.js
  ---
    exit:     143
    timedOut: true
    command:  "node" "settings-test.js"
  ...
```

Because it cannot parse the "command" value, relevant yaml parsing error is:

> expected &lt;block end&gt;, but found Scalar

This fix changes the command value to be one quoted string instead which is
valid:

```
not ok 1 test/settings/settings-test.js
  ---
    exit:     143
    timedOut: true
    command:  "node settings-test.js"
  ...
```

Tests were ran against [InstantTap](http://instanttap.appspot.com/)