Rake tasks errors with Bundler

[mdesantis]

Bundler 2.0 has been released some days ago. not related to Bundler version The Rakefile uses the Bundler constant for some tasks (e.g. rake sandbox) but it doesn't require bundler, causing such tasks to fail with the following error:

$ rake sandbox --trace
** Invoke sandbox (first_time)
** Execute sandbox
rake aborted!
NameError: uninitialized constant Bundler
/home/maurizio/Sviluppo/Nebulab/solidus/Rakefile:108:in `block in <top (required)>'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/task.rb:273:in `block in execute'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/task.rb:273:in `each'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/task.rb:273:in `execute'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/task.rb:214:in `block in invoke_with_call_chain'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/2.6.0/monitor.rb:230:in `mon_synchronize'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/task.rb:194:in `invoke_with_call_chain'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/task.rb:183:in `invoke'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:160:in `invoke_task'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:116:in `block (2 levels) in top_level'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:116:in `each'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:116:in `block in top_level'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:125:in `run_with_threads'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:110:in `top_level'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:83:in `block in run'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:186:in `standard_exception_handling'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib/rake/application.rb:80:in `run'
/home/maurizio/.asdf/installs/ruby/2.6.0/lib/ruby/gems/2.6.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
/home/maurizio/.asdf/installs/ruby/2.6.0/bin/rake:23:in `load'
/home/maurizio/.asdf/installs/ruby/2.6.0/bin/rake:23:in `<main>'
Tasks: TOP => sandbox

Steps to reproduce

gem install bundler -v '2.0.1'
rake sandbox

Expected behavior

The task should successfully complete

Actual behavior

The task fails showing the error above

System configuration

Solidus Version: 2.8.0.alpha / 942ec5c

Extensions in use: none

[kennyadsl]

This is not related to Bundler 2.0 but to not running the command with bundle exec. The proposed fix is still needed though.