Fix typo: Cronologically -> Chronologically

Author: delirious-lettuce

prompt_toolkit/history.py

@@ -27,7 +27,7 @@ def __getitem__(self, key):
 
  @abstractmethod
  def __iter__(self):
- " Iterate through all the items of the history. Cronologically. "
+ " Iterate through all the items of the history. Chronologically. "
 
  @abstractmethod
  def __len__(self):