use TokenBigramSplitSymbolAlphaDigit parser instead of TokenBigramSplitSymbolAlpha by default.

so that we have less misses even though we have more noises.

to migrate, you can use the following SQL :

ALTER TABLE catalog_full_text
  DROP KEY title,
  DROP KEY description,
  ENGINE=mroonga,
  ADD FULLTEXT KEY title (`title`) COMMENT 'parser "TokenBigramSplitSymbolAlphaDigit"',
  ADD FULLTEXT KEY description (`description`) COMMENT 'parser "TokenBigramSplitSymbolAlphaDigit"';

ALTER TABLE content_translation
  DROP KEY translated_text,
  ENGINE=mroonga,
  ADD FULLTEXT KEY translated_text (`translated_text`) COMMENT 'parser "TokenBigramSplitSymbolAlphaDigit"';

ALTER TABLE full_text
  DROP KEY SearchableText,
  ENGINE=mroonga,
  ADD FULLTEXT KEY SearchableText (`SearchableText`) COMMENT 'parser "TokenBigramSplitSymbolAlphaDigit"';