Normalize forward slashes on windows

src/directory.coffee

@@ -65,6 +65,9 @@ class Directory
   relativize: (fullPath) ->
     return fullPath unless fullPath
 
+    # Normalize forward slashes to back slashes on windows
+    fullPath = fullPath.replace(/\//g, '\\') if process.platform is 'windows'
+
     if fullPath is @getPath()
       ''
     else if fullPath.indexOf(path.join(@getPath(), path.sep)) is 0