Can't handle sub-directories

[tomlutzenberger]

I tried to build a xpi package but got the following error:

Running "jpm:run" task
>> Error running Firefox: [Error: Could not parse `package.json` file.
>> ENOENT: no such file or directory, open 'C:\xampp\htdocs\rbutr-browser-extension\dist\package.json']

I placed my prepared (minified etc.) files in a sub-dir named dist/ and jpm tries to read the package.json from there. Is there any workaround or did I do something wrong?
My task looks like this:

jpm: {
    options: {
        src: 'dist/',
        xpi: 'build/'
    }
}