Change the xkcd link in comment over https. (GH-5452)

Lib/antigravity.py

@@ -11,7 +11,7 @@ def geohash(latitude, longitude, datedow):
     37.857713 -122.544543
 
     '''
-    # http://xkcd.com/426/
+    # https://xkcd.com/426/
     h = hashlib.md5(datedow).hexdigest()
     p, q = [('%f' % float.fromhex('0.' + x)) for x in (h[:16], h[16:32])]
     print('%d%s %d%s' % (latitude, p[1:], longitude, q[1:]))