Upgrade Bundler from 1.17.2 to 2.1
With upgrading Ruby from 2.6 to 2.7, upgrade Bundler from 1.17.2 to 2.1. This change will not force user to install Bundler 1.x in the future.
cf. !426 (merged)
Edited by Takuya Noguchi
With upgrading Ruby from 2.6 to 2.7, upgrade Bundler from 1.17.2 to 2.1. This change will not force user to install Bundler 1.x in the future.
cf. !426 (merged)