Add type annotation to ensure_writable

Author: Peter Amstutz

cwltool/pathmapper.py

@@ -169,6 +169,7 @@ def downloadHttpFile(httpurl):
     return f.name
 
 def ensure_writable(path):
+    # type: (Text) -> None
     if os.path.isdir(path):
         for root, dirs, files in os.walk(path):
             for name in files: