Migrate a bbPress WordPress plugin forum to Discourse

I’m getting the following error when I follow the guide and get to the point where I run the import script. I installed discourse as per these instructions

myuser@tmp-discourse:~/discourse$ IMPORT=1 bundle && IMPORT=1 bundle exec ruby script/import_scripts/bbpress.rb

[!] There was an error parsing `Gemfile`: You cannot specify the same gem twice with different version requirements.
You specified: sqlite3 (~> 1.3, >= 1.3.13) and sqlite3 (>= 0). Bundler cannot continue.

 #  from /home/myuser/discourse/Gemfile:251
 #  -------------------------------------------
 #  group :generic_import, optional: true do
 >    gem "sqlite3"
 #    gem "redcarpet"
 #  -------------------------------------------