PYTHON-1420 Fix heartbeatFrequencyMS ConfigurationError.

Author: ShaneHarvey

pymongo/settings.py

@@ -42,8 +42,8 @@ def __init__(self,
  """
  if heartbeat_frequency < common.MIN_HEARTBEAT_INTERVAL:
  raise ConfigurationError(
- "heartbeatFrequencyMS cannot be less than %d" %
- common.MIN_HEARTBEAT_INTERVAL * 1000)
+ "heartbeatFrequencyMS cannot be less than %d" % (
+  common.MIN_HEARTBEAT_INTERVAL * 1000,))
 
  self._seeds = seeds or [('localhost', 27017)]
  self._replica_set_name = replica_set_name