encoding/base64: fix typo in comment
encoding/base64: fix typo in comment

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/258041

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

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