update windows build to Python 3.7

Lib/lib2to3/fixes/fix_basestring.py

@@ -0,0 +1,14 @@
+"""Fixer for basestring -> str."""
+# Author: Christian Heimes
+
+# Local imports
+from .. import fixer_base
+from ..fixer_util import Name
+
+class FixBasestring(fixer_base.BaseFix):
+    BM_compatible = True
+
+    PATTERN = "'basestring'"
+
+    def transform(self, node, results):
+        return Name("str", prefix=node.prefix)