Replace windows path sep with unix sep

It seems python in msys2 has some weird behavior. For __file__, it
returns a string which uses windows-style separator '\', however,
os.path.dirname only recognizes the unix-style separator '/', and
consequently, the path of Mako is not added properly.

components/style/properties/build.py

@@ -6,7 +6,7 @@
 import os.path
 import sys
 
-BASE = os.path.dirname(__file__)
+BASE = os.path.dirname(__file__.replace('\\', '/'))
 sys.path.insert(0, os.path.join(BASE, "Mako-0.9.1.zip"))
 sys.path.insert(0, BASE)  # For importing `data.py`