correct the docstring parameter names to be the same as the variable names

[VladimirFokow]

• The actual parameter name is edge_length but the dosctring had edge_lengths
  (maybe instead should rename the variable edge_length to edge_lengths? - but then it should be renamed everywhere)
• corrected tol in the docstring. It was tolerance

[paulbrodersen]

Thanks for the PR and sorry for the late reply -- I was on vacation, and did not check my github. If you come across any other issues or have any suggestions, do let me know.