Fix typo in docstring

Author: romuald

pymongo/collection.py

@@ -744,7 +744,7 @@ def create_index(self, key_or_list, cache_for=300, **kwargs):
  >>> my_collection.create_index([("mike", pymongo.DESCENDING),
  ... ("eliot", pymongo.ASCENDING)])
 
- All optional index creation paramaters should be passed as
+ All optional index creation parameters should be passed as
  keyword arguments to this method. Valid options include:
 
  - `name`: custom name to use for this index - if none is
@@ -855,7 +855,7 @@ def ensure_index(self, key_or_list, cache_for=300, **kwargs):
  Returns the name of the created index if an index is actually
  created. Returns ``None`` if the index already exists.
 
- All optional index creation paramaters should be passed as
+ All optional index creation parameters should be passed as
  keyword arguments to this method. Valid options include:
 
  - `name`: custom name to use for this index - if none is