conda env create -f environment.yml fails during pip step

MacOS 10.14 Mojave
Miniconda3 (conda 4.8.3)

Following the installation instructions, `conda env create -f environment.yml` fails during the installation of the tokenizers package:

```
error: Can not find Rust compiler
----------------------------------------
ERROR: Failed building wheel for tokenizers
ERROR: Could not build wheels for tokenizers which use PEP 517 and cannot be installed directly

CondaEnvException: Pip failed
```

It seems likely that this is related to the an issue reported for transformers (https://github.com/huggingface/transformers/issues/2831).

Installation of a Rust compiler may be required to proceed. Possibly this can be done through conda?