Revert "Re-add bundler for ruby-2.6"
Revert "Re-add bundler for ruby-2.6"

This reverts commit 0bbb4cf7cb00ecad05e86dcf94badd5836d08a40.

oneclick/rubyinstaller2,larskanis/rubyinstaller2,larskanis/rubyinstaller2,larskanis/rubyinstaller2,oneclick/rubyinstaller2,oneclick/rubyinstaller2