Specify node and yarn versions
Specify node and yarn versions

*Why**: So that production uses the same versions as we use locally. It looks like webpacker (or at least `yarn install`) doesn’t support node > 9 due to upath 1.0.2.

smcgov/SMC-Connect,smcgov/SMC-Connect,smcgov/SMC-Connect,smcgov/SMC-Connect