UtilsSpecs: Unit test corrected

- Use Path.Combine instead of +Path.DirectorySeparatorChar.ToString()+
- Fixes error if HOMEPATH=\ (Root directory, result was 'H:\\' or '//data' on Unix)

tests/Paket.Tests/UtilsSpecs.fs

@@ -15,7 +15,7 @@ let ``createRelativePath should handle spaces``() =
 let ``normalize path with home directory``() =
     "~/data" 
     |> Utils.normalizeLocalPath
-    |> shouldEqual (AbsolutePath (GetHomeDirectory() + Path.DirectorySeparatorChar.ToString()  +  "data"))
+    |> shouldEqual (AbsolutePath (Path.Combine(GetHomeDirectory(), "data")))
 
 [<Test>]
 let ``relative local path is returned as is``() =