hello_bolt: replace TempFile with TempDir
hello_bolt: replace TempFile with TempDir

If TempFile is used cayley.NewGraph complains about
tmpfile.Name() not being a dir.

kortschak/cayley,cayleygraph/cayley,kortschak/cayley,cayleygraph/cayley,kortschak/cayley,kortschak/cayley,kortschak/cayley