Fix linear model warning

[briandesilva]

Changed BaseOptimizer class so that it inherits from sklearn.linear_model.LinearRegression instead of sklearn.linear_model.base.LinearModel. sklearn was throwing a warning that we won't be able to import from sklearn.linear_model.base in the future, i.e.

  /home2/bdesilva/.local/lib/python3.6/site-packages/sklearn/utils/deprecation.py:144: FutureWarning: The sklearn.linear_model.base module is  deprecated in version 0.22 and will be removed in version 0.24. The corresponding classes / functions should instead be imported from sklearn.linear_model. Anything that cannot be imported from sklearn.linear_model is now part of the private API.
    warnings.warn(message, FutureWarning)

I also

• Added sklearn's _rescale_data function which we were also previously importing from sklearn.linear_model.base
• Removed attribute argument being passed to check_is_fitted as it is being deprecated
• Removed extraneous code from sindy.utils.base that was also using LinearRegression
• Reformatted sindy.utils.base with black
• Updated string formatting in sindy.utils.base

[briandesilva]

Sorry, this pull request was meant to be submitted elsewhere.