Bump letter_opener from 1.5.0 to 1.6.0
Bump letter_opener from 1.5.0 to 1.6.0

Bumps [letter_opener](https://github.com/ryanb/letter_opener) from 1.5.0 to 1.6.0.
- [Changelog](https://github.com/ryanb/letter_opener/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ryanb/letter_opener/compare/v1.5.0...v1.6.0)
tigefa/tigefa,tigefa/tigefa,tigefa/tigefa