I can’t get a multiplatform bundler Gemfile to work in JRuby with a
simple raisl3 app.
See: JRuby "bundle install" choking on gem from other platform · Issue #502 · rubygems/bundler · GitHub
for more details.
The only way to start the rails app in jruby seems to be to comment out
the platform-specific parts for other Ruby VMs.