Fix _os.platform is not a function error

[aluanhaddad]

This fixes the _os.platform is not a function exception which occurs when attempting to use the bundle command in jspm@0.17.0-beta. I experimented with local overrides and this did the trick. @frankwallis, @guybedford, does this look right? I was able to reproduce the issue on multiple systems. typescript@1.8.10 works fine with jspm@0.17.0-beta, and typescript@1.9.0-dev works fine when building with jspm@0.16.35.

[frankwallis]

Yes I think that is correct

[guybedford]

Thanks @frankwallis for the confirmation here.

[aluanhaddad]

Thanks!