use forward slash instead of back slash in GF.cabal

GF.cabal

@@ -29,7 +29,7 @@ library
                  bytestring,
                  random
   ghc-options: -O2
-  hs-source-dirs: src\compiler src\runtime\haskell
+  hs-source-dirs: src/compiler src/runtime/haskell
   extensions: 
   exposed-modules: 
     PGF
@@ -86,7 +86,7 @@ executable gf
   else
     build-depends: unix
   ghc-options: -O2
-  hs-source-dirs: src\compiler src\runtime\haskell
+  hs-source-dirs: src/compiler src/runtime/haskell
   extensions:
   main-is: GF.hs
   other-modules: