How to update the vendored packages:

Assuming the govendor tool is available
run the govendor tool from src/cmd directory

  $ go get -u github.com/kardianos/govendor

To update packages used by cmd/pprof:

  $ cd $GOROOT/src/cmd
  $ GOPATH=$GOROOT govendor fetch github.com/google/pprof/...

To update packages used by internal/objfile/*:

  $ GOPATH=$GOROOT govendor fetch golang.org/x/arch/...

GOPATH=$GOROOT in the above commands is a hack to
make govendor work and will create the .cache folder in
$GOROOT as a side-effect. Please make sure to delete
the directory and not to include the directory in the
commit by accident.
