doc: add missing paren (pointed out by nbjoerg)
doc: add missing paren (pointed out by nbjoerg)

R=rsc, r
CC=golang-dev
http://codereview.appspot.com/1983045

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

rflanagan/reginaldflanagan-project1,mhennings/marcohennings-go,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,bryanxu/go-zh,scirelli/scirelli-go,mhennings/marcohennings-go,d0f/go-zh,Triskite/willstone-goclone,mhennings/marcohennings-go,npe9/noahevans-go9,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,rflanagan/reginaldflanagan-project1,bryanxu/go-zh,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,npe9/noahevans-go9,sanjosh/sanjos100-tipc,scirelli/scirelli-go,npe9/noahevans-go9,sanjosh/sanjos100-tipc,webfd/go-zh,scirelli/scirelli-go,d0f/go-zh,Triskite/willstone-goclone,scirelli/scirelli-go,rdp/rogerpack2005-golang,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,webfd/go-zh,scirelli/scirelli-go,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,npe9/noahevans-go9,npe9/noahevans-go9,bryanxu/go-zh,rdp/rogerpack2005-golang,Triskite/willstone-goclone,mhennings/marcohennings-go,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,rdp/rogerpack2005-golang,d0f/go-zh,webfd/go-zh,webfd/go-zh,rdp/rogerpack2005-golang,webfd/go-zh,rflanagan/reginaldflanagan-project1,npe9/noahevans-go9,glycerine/jeaten-go-arrayof-structof,Triskite/willstone-goclone,scirelli/scirelli-go,bryanxu/go-zh,npe9/noahevans-go9,Triskite/willstone-goclone,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,npe9/noahevans-go9,rdp/rogerpack2005-golang,webfd/go-zh,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,mhennings/marcohennings-go,scirelli/scirelli-go,Triskite/willstone-goclone