doc: change invalid otp response code to 400 (#1863)
doc: change invalid otp response code to 400 (#1863)

invalid otp response code is 400 bad request.
chrishoffman/vault,lirao/vault,Aloomaio/vault,quixoten/vault,joelthompson/vault,mymercurialsky/vault,mgk/vault,MonsantoCo/vault,Caiyeon/vault,ryon/vault,hashicorp/vault,hashicorp/vault,hashicorp/vault,rnaveiras/vault,hashicorp/vault,jgcallero/vault,jam-pot/vault,mgk/vault,martin-ducar-gd/vault,hartsock/vault,quixoten/vault,Banno/vault,Aloomaio/vault,kingland/vault,naunga/vault,kingland/vault,Banno/vault,jmhardison/vault,hashicorp/vault,deverton/hashicorp-vault,jmhardison/vault,quixoten/vault,hartsock/vault,doodles526/vault,hashicorp/vault,kingland/vault,jmhardison/vault,danielsomerfield/vault,jgcallero/vault,martin-ducar-gd/vault,lemondrank/vault,ryon/vault,michaelansel/vault,mgk/vault,chrishoffman/vault,jam-pot/vault,LolalyLuo/vault,rnaveiras/vault,cimarron-pistoncloud/vault,kingland/vault,wjam/vault,deverton/hashicorp-vault,mgk/vault,wjam/vault,lemondrank/vault,joelthompson/vault,quixoten/vault,LolalyLuo/vault,rnaveiras/vault,doodles526/vault,memory/vault,tallpauley/vault,naunga/vault,danielsomerfield/vault,lirao/vault,jmhardison/vault,michaelansel/vault,joelthompson/vault,mymercurialsky/vault,rnaveiras/vault,tallpauley/vault,cimarron-pistoncloud/vault,hartsock/vault,joelthompson/vault,Caiyeon/vault,Aloomaio/vault,memory/vault,rnaveiras/vault,kingland/vault,hartsock/vault,Aloomaio/vault,hartsock/vault,MonsantoCo/vault,jmhardison/vault