Update symfony to latest security release
Update symfony to latest security release

See https://symfony.com/blog/cve-2017-11365-empty-passwords-validation-issue
for more info on the security issue

tvlooy/SecretSanta,wimme002/SecretSanta,TomCan/SecretSanta,tvlooy/SecretSanta,acrobat/SecretSanta,acrobat/SecretSanta,wimme002/SecretSanta,tvlooy/SecretSanta,Intracto/SecretSanta,wimme002/SecretSanta,Intracto/SecretSanta,tvlooy/SecretSanta,TomCan/SecretSanta,TomCan/SecretSanta,acrobat/SecretSanta,Intracto/SecretSanta,wimme002/SecretSanta,acrobat/SecretSanta,Intracto/SecretSanta,TomCan/SecretSanta