Declare 'err' because Python 3 has stricter scoping rules

I Python 3, __err__ will go out of scope after the __try / except__ block.  This change preserves the value after the end of the __try / except__ block.

src/main.py

@@ -208,6 +208,7 @@ class Actions(object):
         for content_inner_path in site.content_manager.contents:
             s = time.time()
             logging.info("Verifing %s signature..." % content_inner_path)
+            err = None
             try:
                 file_correct = site.content_manager.verifyFile(
                     content_inner_path, site.storage.open(content_inner_path, "rb"), ignore_same=False