Dont use shellwords with windows

> Shellwords

> Manipulates strings like the UNIX Bourne shell¶ ↑

> This module manipulates strings according to the word parsing rules of the UNIX Bourne shell.

> The shellwords() function was originally a port of shellwords.pl, but modified to conform to POSIX / SUSv3 (IEEE Std 1003.1-2001 [1]).

Shellwords obeys posix rules, these don't seem to work on Windows, (#1713) so we should do something differently on Windows.
Right, the problem is that it was not included in rspec-support 3.1.0.  All rspec-core 3.1.x releases have to be compatible with all rspec-support 3.1.x releases.  We don't declare patch-level dependencies in the gemspec and I don't want to start doing that.