Suggester string_distance option typo in code

[mimitsu]

The string_distance option for suggesters has 5 options. The default is demarau_levenshtein. That's okay. One of the other options is the more classic levenstein. That's without the h. I think the Levenshtein of Demarau-Levenshtein is the same dude who came up with the LevensHtein distance.

I thought maybe it was just a typo in the documentation, but I just tested it on 6.0.0-rc1.

I'm guessing not many people use this option so nobody noticed.