Add tm_zone and tm_gmtoff to time.pyi (#551)

* Enable tm_gmtoff and tm_zone only for python >= 3.3.

stdlib/3/time.pyi

@@ -4,6 +4,7 @@
 # based on: http://docs.python.org/3.2/library/time.html#module-time
 # see: http://nullege.com/codes/search?cq=time
 
+import sys
 from typing import Tuple, Union
 
 # ----- variables and constants -----
@@ -32,7 +33,9 @@ class struct_time:
     tm_wday = 0
     tm_yday = 0
     tm_isdst = 0
-
+    if sys.version_info >= (3, 3):
+        tm_gmtoff = 0
+        tm_zone = 'GMT'
 
 # ----- functions -----
 def asctime(t: Union[Tuple[int, int, int, int, int, int, int, int, int],