Update validator requirement from 0.14 to 0.15
Update validator requirement from 0.14 to 0.15

Updates the requirements on [validator](https://github.com/Keats/validator) to permit the latest version.
- [Release notes](https://github.com/Keats/validator/releases)
- [Changelog](https://github.com/Keats/validator/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Keats/validator/compare/v0.14.0...v0.15.0)

---
updated-dependencies:
- dependency-name: validator
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
svenstaro/rust-web-boilerplate,svenstaro/rust-web-boilerplate