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.
This is OK for master but when we backport this to 3-1-maintenance (assuming we merge this), this'll need to not use this method from rspec-support because it's not in rspec-support 3.1.0 and we need to keep all patch versions from the same minor version working together.  You can just put the same conditional logic from `RSpec::Support::OS.windows?` inline here.