Fixed compilation with GHC 8.6.1-alpha2.

Author: asr

unix-compat.cabal

@@ -63,7 +63,7 @@ Library
       System.PosixCompat.Internal.Time
 
   else
-    build-depends: unix >= 2.4 && < 2.8
+    build-depends: unix >= 2.4 && < 2.9
     include-dirs: include
     includes: HsUnixCompat.h
     install-includes: HsUnixCompat.h