Generating protobuf sources

[Daniel McKenna]

I've been trying to figure this out but wracking my brains slightly, I'm trying to add a new proto to the project for a PR. But when I run the proto code gen binary I get:

```

Error: Custom { kind: Other, error: "protoc (\"/usr/bin/protoc\" \"-I/home/xd009642/code/rust/tensorflow/target/tensorflow/tensorflow\" \"--descriptor_set_out=/tmp/protoc-rustSWZtMd/descriptor.pbbin\" \"--include_imports\" \"/home/xd009642/code/rust/tensorflow/target/tensorflow/tensorflow/tensorflow/core/framework/attr_value.proto\" 

...

\"/home/xd009642/code/rust/tensorflow/target/tensorflow/tensorflow/tensorflow/core/framework/versions.proto\" \"/home/xd009642/code/rust/tensorflow/target/tensorflow/tensorflow/tensorflow/core/protobuf/meta_graph.proto\" \"/home/xd009642/code/rust/tensorflow/target/tensorflow/tensorflow/tensorflow/core/protobuf/saver.proto\") exited with non-zero exit code" }

```

I've cut out some of the lines for brevity, but there doesn't seem to be any useful diagnostics

[Daniel McKenna]

Also using protoc 3.6.1. I'll update tomorrow and see if that solves it

[Daniel McKenna]

Yeah proto version did it. All good now