doc: fixing field name to security_token (#1850)
doc: fixing field name to security_token (#1850)

response field is security_token, not secret_token.
joelthompson/vault,rnaveiras/vault,Banno/vault,kingland/vault,mymercurialsky/vault,joelthompson/vault,hartsock/vault,joelthompson/vault,tallpauley/vault,martin-ducar-gd/vault,chrishoffman/vault,hashicorp/vault,wjam/vault,hartsock/vault,lemondrank/vault,kingland/vault,LolalyLuo/vault,quixoten/vault,martin-ducar-gd/vault,deverton/hashicorp-vault,hashicorp/vault,cimarron-pistoncloud/vault,hashicorp/vault,LolalyLuo/vault,danielsomerfield/vault,mgk/vault,Banno/vault,MonsantoCo/vault,ryon/vault,kingland/vault,Aloomaio/vault,hashicorp/vault,jmhardison/vault,jam-pot/vault,jmhardison/vault,danielsomerfield/vault,Aloomaio/vault,tallpauley/vault,jam-pot/vault,quixoten/vault,hashicorp/vault,rnaveiras/vault,naunga/vault,chrishoffman/vault,quixoten/vault,jmhardison/vault,Caiyeon/vault,ryon/vault,doodles526/vault,MonsantoCo/vault,hashicorp/vault,michaelansel/vault,lirao/vault,mgk/vault,kingland/vault,quixoten/vault,memory/vault,michaelansel/vault,jgcallero/vault,cimarron-pistoncloud/vault,mymercurialsky/vault,jmhardison/vault,wjam/vault,rnaveiras/vault,hartsock/vault,deverton/hashicorp-vault,doodles526/vault,jgcallero/vault,rnaveiras/vault,lirao/vault,mgk/vault,Aloomaio/vault,naunga/vault,rnaveiras/vault,Aloomaio/vault,hartsock/vault,Caiyeon/vault,mgk/vault,joelthompson/vault,lemondrank/vault,hartsock/vault,memory/vault,jmhardison/vault,kingland/vault