beta-regression: evm-stateful "may not live long enough"

[Discovered by crater](https://crater-reports.s3.amazonaws.com/beta-1.31-2/beta-2018-11-13/reg/evm-stateful-0.9.2/log.txt) reproducible with:

```
$ git clone git clone https://source.that.world/source/evm-rs/
$ cd evm-rs/stateful
$ cargo +beta test
```

cc @rust-lang/compiler, cc @sorpaas