doc/reference-cmd: use vet as example, not fmt "go tool fmt" doesn't work, "go tool vet" does.
doc/reference-cmd: use vet as example, not fmt
"go tool fmt" doesn't work, "go tool vet" does.

R=golang-dev, rogpeppe, r, minux.ma, bradfitz
CC=golang-dev
http://codereview.appspot.com/5900049

Triskite/willstone-goclone,d0f/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,scirelli/scirelli-go,webfd/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,d0f/go-zh,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,Triskite/willstone-goclone,mhennings/marcohennings-go,webfd/go-zh,mhennings/marcohennings-go,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,mhennings/marcohennings-go,webfd/go-zh,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,Triskite/willstone-goclone,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,webfd/go-zh,scirelli/scirelli-go,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,bryanxu/go-zh,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,webfd/go-zh,bryanxu/go-zh,scirelli/scirelli-go,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,d0f/go-zh,sanjosh/sanjos100-tipc,scirelli/scirelli-go,d0f/go-zh,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,Triskite/willstone-goclone,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,Triskite/willstone-goclone,mhennings/marcohennings-go,webfd/go-zh,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,scirelli/scirelli-go,rdp/rogerpack2005-golang,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,bryanxu/go-zh