Flush at the end of tf_gen
Flush at the end of tf_gen

OCaml doesn't appear to guarantee flushing on exit, and said flushing doesn't
fire in my setup.  Thus, do it manually.

hhugo/tensorflow-ocaml,LaurentMazare/tensorflow-ocaml,hhugo/tensorflow-ocaml,LaurentMazare/tensorflow-ocaml