Log Message:
misc/ruby-bundler: update to 2.2.15

2.2.15 (March 19, 2021)

Enhancements:

* Add a hint about bundler installing executables for path gems #4461
* Warn lockfiles with incorrect resolutions #4459
* Don't generate duplicate redundant sources in the lockfile #4456

Bug fixes:

* Respect running ruby when resolving platforms #4449