Redmine

I installed Redmine using the installation guide found on the main Redmine page. That guide had me download and compile Ruby from source (2.5.0). Along with that compilation, the needed gems were downloaded/installed. One of those was rspec version 2.99.0.

Now, we have some users that are using Mantis for another project, and I want to migrate that data using the migrate_from_mantis.rake method. When I run this, I get the following error:

rake aborted!
NoMethodError: undefined method `last_comment' for #<Rake::Application:0x000055c17fb22898>
/var/www/html/redmine/Rakefile:7:in `<top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'
(See full trace by running task with --trace)

In doing some research, I've read that rspec 3.4.4 fixes this. However, I don't know how to update it to this version (I'm VERY new to Ruby and gems). It appears like the repository for gem installation is set to the local Ruby area where the install guide had me build, so I keep getting told that rspec is at the latest available version.

So, how do I point my redmine installation to a repository with new gems so I can update rspec, and thereby, get migrate_from_mantis.rake to run successfully?

Thanks,
Harry