Update striptags requirement from ^2.1.1 to ^3.1.1
Update striptags requirement from ^2.1.1 to ^3.1.1

Updates the requirements on [striptags](https://github.com/ericnorris/striptags) to permit the latest version.
- [Release notes](https://github.com/ericnorris/striptags/releases)
- [Commits](https://github.com/ericnorris/striptags/commits/v3.1.1)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
hexojs/hexo-util,hexojs/hexo-util