Fix ParameterCollection.where docstring

armi/reactor/parameters/parameterCollections.py

@@ -497,7 +497,7 @@ def restoreBackup(self, paramsToApply):
  def where(
  self, f: Callable[[parameterDefinitions.Parameter], bool]
  ) -> Iterator[parameterDefinitions.Parameter]:
- """Produce an iterator over parameters that meet some criteria
+ """Produce an iterator over parameters that meet some criteria.
 
  Parameters
  ----------