Argument description in rulefit.py needs corrected

[caseywhorton]

Hello! The description of exclude_zero_coef on line 557 in rulefit.py states that True is the default, but False looks to be the default for the argument in the function:

exclude_zero_coef: If True (default), returns only the rules with an estimated coefficient not equalt to zero.

https://github.com/christophM/rulefit/blob/b1657af4b41df59e2ae64bb1767dbaf5ff1ed7fe/rulefit/rulefit.py#L557