babel presets not being used during postinstall

I've encountered an issue where a library I've made that relies on Webpack and the Babel "react" preset, and relies on postinstall-build to build in dependent projects, fails when built there. Here's a trimmed down version that reproduces the issue:

https://github.com/bdefore/postinstall-build-error-dependent
https://github.com/bdefore/postinstall-build-error-library

The library project can successfully run `npm run build:react` but when it does so in the postinstall step of the dependent project, it fails to parse JSX.

Here's a gist of the terminal output of the failure: https://gist.github.com/bdefore/cb4269649b7e3e4e42dcf1f52d573f9a

The full npm-debug.log is checked in here: https://raw.githubusercontent.com/bdefore/postinstall-build-error-dependent/master/npm-debug.log