Migrating to bootstrap 4.0.0.alpha6 would involve further changes in _type.scss.erb ($font-size-root is not available anymore) and all dependents because Bootstrap 4 switches from px-based to rem-based font sizes (see https://github.com/twbs/bootstrap/issues/19943).
Furthermore, rebuilding the Gemfile.lock on UNIX prevents Heroku from throwing away the Windows-based lock file in future builds. Notice that this includes updating some other gems in their minor versions.
Migrating to
bootstrap 4.0.0.alpha6would involve further changes in_type.scss.erb($font-size-rootis not available anymore) and all dependents because Bootstrap 4 switches from px-based to rem-based font sizes (see https://github.com/twbs/bootstrap/issues/19943).Furthermore, rebuilding the
Gemfile.lockon UNIX prevents Heroku from throwing away the Windows-based lock file in future builds. Notice that this includes updating some other gems in their minor versions.