Link IRB back to StdLib.
    
    This avoids issues running `$ bin/rails console --sandbox`, which
    otherwise breaks with error such as:
    
    ~~~
    $ bin/rails console --sandbox
    Traceback (most recent call last):
    	12: from bin/rails:4:in `<main>'
    	11: from bin/rails:4:in `require'
    	10: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/commands.rb:18:in `<top (required)>'
    	 9: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/command.rb:44:in `invoke'
    	 8: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/command.rb:70:in `find_by_namespace'
    	 7: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/command/behavior.rb:79:in `lookup'
    	 6: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/command/behavior.rb:79:in `each'
    	 5: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/command/behavior.rb:80:in `block in lookup'
    	 4: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/command/behavior.rb:80:in `each'
    	 3: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/command/behavior.rb:84:in `block (2 levels) in lookup'
    	 2: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/command/behavior.rb:84:in `require'
    	 1: from /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/commands/console/console_command.rb:3:in `<top (required)>'
    /builddir/.gem/ruby/gems/railties-5.2.2.1/lib/rails/commands/console/console_command.rb:3:in `require': cannot load such file -- irb (LoadError)
    ~~~