Make doctest pass by specifying the right encoding.

Lib/doctest.py

@@ -210,7 +210,7 @@ def _load_testfile(filename, package, module_relative):
         if hasattr(package, '__loader__'):
             if hasattr(package.__loader__, 'get_data'):
                 return package.__loader__.get_data(filename), filename
-    return open(filename).read(), filename
+    return open(filename, encoding="utf-8").read(), filename
 
 def _indent(s, indent=4):
     """