Build not finding modules from `node_modules`

[pittst3r]

$ yarn build
yarn build v0.17.6
$ rm -rf dist && BROCCOLI_ENV=dist broccoli build dist
Build project: @glimmer/di
Build env: dist
Build path: /wouldnt/you/like/to/know/glimmer-di
/src/container.ts(4,28): Cannot find module 'glimmer-util'.
/src/registry.ts(1,28): Cannot find module 'glimmer-util'.
✨  Done in 3.31s.

Probably because we're not including node_modules when building:

let tsinclude = [
  'src/**',
  'lib.*.d.ts'
];

// ...

let ts = funnel(mergeTrees([libs, projectPath]), {
  include: tsinclude,
  annotation: 'raw source'
});