Fix chaining validators
Fix chaining validators

https://github.com/chriso/node-validator/commit/3bca87306e43572ba3643e56
6c662f474747466c
Above commit from node-validator@0.4.6-2 rendered express_validator
buggy when chaining validators got error. Required to return itself
instead of undefined.

jg3526/express-validator,ctavan/express-validator,ctavan/express-validator,h3dx0/express-validator,AndrasEszes/express-validator,phuson/express-validator,Jakeii/express-validator,carlitux/koa-async-validator,ghostRider1124/express-validator,supasate/express-validator