Use an sh-compatible construct

[deivid-rodriguez]

As requested by @nickcharlton here. I couldn't run the tests locally since I get this error:

Bundler::GemNotFound: Could not find gem 'simple_form' in any of the gem sources listed in your Gemfile.
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/resolver.rb:376:in `block in verify_gemfile_dependencies_are_found!'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/resolver.rb:346:in `each'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/resolver.rb:346:in `verify_gemfile_dependencies_are_found!'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/resolver.rb:201:in `start'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/resolver.rb:181:in `resolve'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/definition.rb:251:in `resolve'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/definition.rb:175:in `specs'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/definition.rb:234:in `specs_for'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/definition.rb:223:in `requested_specs'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/runtime.rb:118:in `block in definition_method'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/runtime.rb:19:in `setup'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler.rb:102:in `setup'
/home/deivid/.gem/ruby/2.4.0/gems/bundler-1.14.0.pre.2/lib/bundler/setup.rb:20:in `<top (required)>'
/home/deivid/Code/suspenders/tmp/dummy_app/config/boot.rb:3:in `<top (required)>'
/home/deivid/Code/suspenders/tmp/dummy_app/config/application.rb:1:in `require_relative'
/home/deivid/Code/suspenders/tmp/dummy_app/config/application.rb:1:in `<top (required)>'
/home/deivid/Code/suspenders/tmp/dummy_app/Rakefile:4:in `require_relative'
/home/deivid/Code/suspenders/tmp/dummy_app/Rakefile:4:in `<top (required)>'
/home/deivid/.gem/ruby/2.4.0/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'
LoadError: cannot load such file -- bundler/setup
/home/deivid/Code/suspenders/tmp/dummy_app/config/boot.rb:3:in `<top (required)>'
/home/deivid/Code/suspenders/tmp/dummy_app/config/application.rb:1:in `require_relative'
/home/deivid/Code/suspenders/tmp/dummy_app/config/application.rb:1:in `<top (required)>'
/home/deivid/Code/suspenders/tmp/dummy_app/Rakefile:4:in `require_relative'
/home/deivid/Code/suspenders/tmp/dummy_app/Rakefile:4:in `<top (required)>'
/home/deivid/.gem/ruby/2.4.0/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'

But I guess this doesn't break anything.

[tute]

Thank you! :)

[deivid-rodriguez]

Welcome!