message: Mention additional memory needed by node in docs.
diff: 1. Edit `dependency-map.json` and bump every `^3.0.0-pre.<N>` version to
  `^3.0.0-pre.<N+1>`.
  -2. Run `modulizer --clean --npm-version 3.0.0-pre.<N+1> --repo $(cat <modulizer dir>/docs/polymer-modulize-repos.txt | tr '\n' ' ') --delete-files bower.json '**/*.d.ts' types/`. This should take 2-3 minutes.
  +2. Run `NODE_OPTIONS="--max_old_space_size=8192" modulizer --clean --npm-version 3.0.0-pre.<N+1> --repo $(cat <modulizer dir>/docs/polymer-modulize-repos.txt | tr '\n' ' ') --delete-files bower.json '**/*.d.ts' types/`. This should take 2-3 minutes.
  3. Choose *"Install dependencies and run tests"*. This should take 15-20 minutes.
  Expect only Chrome tests to pass (see [#291](https://github.com/Polymer/polymer-modulizer/issues/291)). Look at the [Element status](https://github.com/Polymer/polymer-modulizer/blob/master/docs/polymer-3-element-status.md) doc and spot check that 5-10 elements that were previously passing are still passing.
  