Bug: `string:levenshteinDistance` can sometimes produce incorrect results

[Yewzir]

I just noticed that the results of string:levenshteinDistance are sometimes incorrect, probably because the implementation counts an extra character operation, albeit incorrectly. I have collected a number of examples for you in which this discrepancy occurs.

_str1	_str2	Output	Expected
before	order	6	5
time	system	6	5
state	present	7	6
square	consider	8	7
after	carbohydrate	11	10
dictionary	general	10	9
incomprehensible	public	15	14
under	square	6	5
there	number	6	5
there	never	5	4
structure	interest	9	8
possible	public	7	6

As you can see, one extra character operation is counted with the above parameters.