remove dev flag from examples

[bdefore]

Fixes #191

Proposed Changes

Removed all references of :dev from examples

Description

Per https://github.com/meltwater/drone-cache/issues/157#issuecomment-778297766 we shouldn't be using dev images and they're out of date.

Checklist

• [x] Read the CONTRIBUTING document.
• [x] Read the CODE OF CONDUCT document.
• [x] Ensure your code follows the code style of this project.
• [ ] Ensure CI and all other PR checks are green OR
  • [ ] Code compiles correctly.
  • [ ] Created tests which fail without the change (if possible).
  • [ ] All new and existing tests passed.
• [x] Add your changes to Unreleased section of CHANGELOG.
• [x] Improve and update the README (if necessary).
• [x] Ensure documentation is up-to-date. The same file will be updated in plugin index when your PR is accepted, so it will be available for end-users at http://plugins.drone.io.