Windows/msi: Fix msi build issue with WiX 3.7/3.8

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Fix the msi build with Wix 3.7/3.8 where I ran into the following error:

C:\Users\Raymond Feng\Projects\thirdparty\node\tools\msvs\msi\product.wxs(139):
error LGHT0094: Unresolved reference to symbol 'WixComponentGroup:Product.Gene
rated' in section 'Product:*'. [C:\Users\Raymond Feng\Projects\thirdparty\node\
tools\msvs\msi\nodemsi.wixproj]

The fix was based on:

http://windows-installer-xml-wix-toolset.687559.n2.nabble.com/How-to-get-heat-exe-to-harvest-td7473250.html

I have signed CLA under name "Zhaohui Feng (aka Raymond Feng)".