tests use cross-spawn-async instead of child_process.spawn
tests use cross-spawn-async instead of child_process.spawn

This allows Windows to run the tests, as promised in
https://github.com/feross/webtorrent/issues/429#issuecomment-146061289

Note that there are a couple of outstanding failures on Windows:

    # client.seed: filesystem path to folder with one file, string
    not ok 8 should be equal
      ---
        operator: equal
        expected: '3a686c32404af0a66913dd5f8d2b40673f8d4490'
        actual:   'e6887b78d89d995876c7cef3476b6fb32c4c4e3d'
      ...
    not ok 9 should be equal
      ---
        operator: equal
        expected: |-
          'magnet:?xt=urn:btih:3a686c32404af0a66913dd5f8d2b40673f8d4490&dn=folder&tr=udp%3A%2F%2Ftracker.webtorrent.io%3A80'
        actual: |-
          'magnet:?xt=urn:btih:e6887b78d89d995876c7cef3476b6fb32c4c4e3d&dn=folder&tr=udp%3A%2F%2Ftracker.webtorrent.io%3A80'

feross/webtorrent-cli,feross/webtorrent-cli