DictionarySlugCreator may create invalid slug

[hata6502]

When converted prh to proofdict by prh-to-proofdict, some converted file names are invalid.

Input prh files
https://github.com/azu/prh.yml/tree/master/ja

• kanji-open.yml
• spoken.yml
• typo.yml
• web+db.yml

To fix these, I replaced to number order file names.

hata6502/proof-dictionary@4812f68

I think that escaping all patterns for file name is hard!
Thank you for maintaining :)