VFSImporter: replace deprecated U open() flag

Fixes #1063

direct/src/showbase/VFSImporter.py

@@ -65,7 +65,7 @@ class VFSImporter:
         vfile = vfs.getFile(filename, True)
         if vfile:
             return VFSLoader(dir_path, vfile, filename,
-                             desc=('.py', 'U', imp.PY_SOURCE))
+                             desc=('.py', 'r', imp.PY_SOURCE))
 
         # If there's no .py file, but there's a .pyc file, load that
         # anyway.
@@ -93,7 +93,7 @@ class VFSImporter:
         vfile = vfs.getFile(filename, True)
         if vfile:
             return VFSLoader(dir_path, vfile, filename, packagePath=path,
-                             desc=('.py', 'U', imp.PY_SOURCE))
+                             desc=('.py', 'r', imp.PY_SOURCE))
         for ext in compiledExtensions:
             filename = Filename(path, '__init__.' + ext)
             vfile = vfs.getFile(filename, True)