Update suggested strength.


I'm updating from 4k to around 120k rounds, according to 

"OWASP recommends hashing the password at least 64,000 times in 2012, and doubling that every two years, per https://www.owasp.org/index.php/Password_Storage_Cheat_Sheet"

http://crypto.stackexchange.com/questions/3484/pbkdf2-and-salt
Merge pull request #15 from alexanderkjeldaas/patch-1

Update suggested strength.