api: Fix undefined variable reference from previous commit.

Author: mateuszmandera

zulip/zulip/__init__.py

@@ -95,7 +95,7 @@ def fail(self):
         # Exponential growth with ratio sqrt(2); compute random delay
         # between x and 2x where x is growing exponentially
         delay_scale = int(2 ** (self.number_of_retries / 2.0 - 1)) + 1
-        delay = min(delay_scale + random.randint(1, delay_scale), delay_cap)
+        delay = min(delay_scale + random.randint(1, delay_scale), self.delay_cap)
         message = "Sleeping for %ss [max %s] before retrying." % (delay, delay_scale * 2)
         try:
             logger.warning(message)