Use existing cabal.project in appveyor

Author: hasufell

appveyor.yml

@@ -76,15 +76,12 @@ before_build:
  - rmdir /Q /S dist-newstyle
 
 build_script:
- - echo packages:. > cabal.project
- - cabal configure --allow-newer --ghc-options="-Werror"
  - cabal %CABOPTS% build -j all --ghc-options="-Werror"
  # Build from sdist if required.
  - ps: >-
     If ($env:PKG_TEST -Match "yes") {
        cabal sdist
-       echo "packages: dist-newstyle/sdist/*.tar.gz" | Out-File -Encoding ASCII cabal.project
+       ((Get-Content -path cabal.project -Raw) -replace "packages: .", "packages: dist-newstyle/sdist/*.tar.gz") | Set-Content -Path cabal.project
        cat cabal.project
-       cabal configure --allow-newer --ghc-options="-Werror"
        cabal $env:CABOPTS build -j pkg:Win32 --ghc-options="-Werror"
     }

cabal.project

@@ -0,0 +1,2 @@
+packages: .
+          https://hackage.haskell.org/package/filepath-1.4.99.5/candidate/filepath-1.4.99.5.tar.gz