Update morfologik-stemming dependency to 1.8.1

Hi folks.

This patch improves sanity checking of input dictionaries (previously broken slovak.dict) and contains a bunch of other improvements. I also fixed option handling in the code of DictionaryBuilder. This patch also piggybacks a fix to slovak.dict which was previously broken (contained an unencodeable entry) -- the dictionary is recompressed with the new length-optimal prefix encoding. Note fsa.dict.uses-* properties are still supported, but are deprecated in favor of:

fsa.dict.encoder=[prefix|infix|suffix|none]

declaration.