[CSL-789] Force Appveyor cache overwrite using xcopy /y
[CSL-789] Force Appveyor cache overwrite using xcopy /y

input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype