Fix build script on windows.

The build and trace output is useless, but here it is anyway:
```
>jake --trace
Checking for JS errors...
jake aborted.
Error: '.' is not recognized as an internal or external command,
operable program or batch file.
    at api.fail (C:\Users\dave\AppData\Roaming\npm\node_modules\jake\lib\api.js:326:18)
    at null.<anonymous> (C:\Users\dave\AppData\Roaming\npm\node_modules\jake\lib\utils\index.js:134:9)
    at EventEmitter.emit (events.js:98:17)
    at ChildProcess.<anonymous> (C:\Users\dave\AppData\Roaming\npm\node_modules\jake\lib\utils\index.js:210:20)
    at ChildProcess.EventEmitter.emit (events.js:98:17)
    at Process.ChildProcess._handle.onexit (child_process.js:789:12)
```