Everything is correct, since 1.9.2dev
version is prior to 1.9.2
:
irb > Gem::Version.new('1.9.2dev') >= Gem::Version.new('1.9.2')
# => false
irb > Gem::Version.new('1.9.2dev') >= Gem::Version.new('1.9.1')
# => true
As a temporary workaround you may try to install bundler
explicitly:
gem install bundler
Apparently I would suggest you to upgrade Ruby in any case, dev
versions are definitely not the best choice to deal with.