go.crypto/blowfish: fix typo in docstring in cipher.go
go.crypto/blowfish: fix typo in docstring in cipher.go

Change-Id: I1b968decc23de5b7f635dcbc4133b1ab3745ff88
Reviewed-on: https://go-review.googlesource.com/23851
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/crypto,ScriptRock/crypto,mattharden/crypto,golang/crypto,mattharden/crypto,ScriptRock/crypto,golang/crypto