[Support-753] Fix Rakefile for Windows users

Description of your patch
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Fix Rakefile for Windows users

Recommended Release Notes
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Minor fix for Windows users

Estimated risk
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Low

Components involved
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Rakefile

Description of testing done
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`rake new_cookbook COOKBOOK=test_recipe` on OS X, Linux and Windows.

QA Instructions
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Locate a Windows computer or VM
Install Ruby on it (http://railsinstaller.org/en has an installer that includes Git)
Clone ey-cloud-recipes locally
run `rake new_cookbook COOKBOOK=test_recipe` 
Verify it completes successfully (previously complained ` /p is not a valid flag`)