text: Title: Argument to PredictionError is overwritten
  Body: **Describe the bug**
  Argument `is_fitted` is overwritten when Instantiating a `PredictionError` or  `ResidualsPlot`.
  
  **To Reproduce**
  
  ```python
  from yellowbrick.regressor import PredictionError
  from sklearn.linear_models import Lasso
  
  visualizer = PredictionError(Lasso(), "test title", is_fitted=True)
  print(visualizer.is_fitted)
  ```
  
  **Expected behavior**
  When `is_fitted` is passed in, I expect it to not be overwritten in the __init__ calls
  
  
  **Desktop (please complete the following information):**
   - OS: Ubuntu 20.04
   - Python Version 3.8.10
   - Yellowbrick Version :  1.3.post1
  
  