Import updated regular expression for Subject header from https://github.com/sisimai/p5-Sisimai/commit/8015fcb49e4741d988f476a38267f29d8bd0a3f4
Import updated regular expression for Subject header from https://github.com/sisimai/p5-Sisimai/commit/8015fcb49e4741d988f476a38267f29d8bd0a3f4

azumakuniyuki/rb-Sisimai,azumakuniyuki/rb-Sisimai