How to downgrade bundler or upgrade rails?

Try the following commands:

gem uninstall bundler
gem install bundler --version '1.0.0'

To install downgraded version of bundler, try:

gem install bundler --version '<= 0.10.6'

so you could have both version installed (check: gem list bundler/bundler _0.9.26_ -v), then run using that specific version, e.g.:

bundle _0.9.26_ install

Learn more: How to upgrade/downgrade Rubygems at rubyforge

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