Make `ErrorResponse` implement `Error`
Make `ErrorResponse` implement `Error`

This allows an ErrorResponse to be used directly as an error type.

Signed-off-by: Brian Goff <dc73d0991b982a8303e713ef531a313af77e242a@gmail.com>

jthelin/docker,kojiromike/docker,mahak/docker,konstruktoid/docker-1,moby/moby,SvenDowideit/docker,crosbymichael/docker,nalind/docker,mahak/docker,Mokolea/docker,bearstech/moby,moul/docker,flavio/docker,konstruktoid/docker-upstream,crosbymichael/docker,jvanz/docker,dims/docker,djs55/docker,yongtang/docker,docker/docker,trebonian/docker,yosifkit/docker,gnailuy/docker,Mokolea/docker,jthelin/docker,kolyshkin/moby,ibuildthecloud/docker,konstruktoid/docker-upstream,justincormack/docker,mahak/docker,ibuildthecloud/docker,unclejack/docker,cpuguy83/docker,dims/docker,moul/docker,djs55/docker,flavio/docker,SvenDowideit/docker,AkihiroSuda/docker,estesp/docker,gnailuy/docker,paralin/docker,jimjag/docker,mahak/docker,vdemeester/docker,docker/docker,thaJeztah/docker,kojiromike/docker,jameszhan/docker,konstruktoid/docker-upstream,Ramzec/docker,jimjag/docker,moby/moby,thaJeztah/docker,justincormack/docker,pradipd/moby,AkihiroSuda/docker,nalind/docker,konstruktoid/docker-1,nawawi/docker,moul/docker,yosifkit/docker,cpuguy83/docker,trebonian/docker,paralin/docker,justincormack/docker,SvenDowideit/docker,ibuildthecloud/docker,Ramzec/docker,jimjag/docker,flavio/docker,bearstech/moby,paralin/docker,kolyshkin/moby,AkihiroSuda/docker,nawawi/docker,bearstech/moby,vdemeester/docker,jimjag/docker,jvanz/docker,estesp/docker,estesp/docker,paralin/docker,yosifkit/docker,konstruktoid/docker-upstream,Mokolea/docker,konstruktoid/docker-1,pradipd/moby,thaJeztah/docker,flavio/docker,jameszhan/docker,jvanz/docker,cpuguy83/docker,djs55/docker,vdemeester/docker,Ramzec/docker,cpuguy83/docker,yosifkit/docker,yongtang/docker,dims/docker,gnailuy/docker,pradipd/moby,nawawi/docker,tmp6154/docker,docker/docker,moul/docker,thaJeztah/docker,nawawi/docker,crosbymichael/docker,moby/moby,Ramzec/docker,bearstech/moby,yongtang/docker,gnailuy/docker,unclejack/docker,trebonian/docker,ibuildthecloud/docker,kolyshkin/moby,tmp6154/docker,trebonian/docker,tmp6154/docker,Mokolea/docker,kojiromike/docker,unclejack/docker,jameszhan/docker,AkihiroSuda/docker,nalind/docker,moby/moby,ibuildthecloud/docker,nalind/docker