Update actix requirement from =0.7.5 to =0.7.6 (#1033)
Update actix requirement from =0.7.5 to =0.7.6 (#1033)

Updates the requirements on [actix](https://github.com/actix/actix) to permit the latest version.
- [Release notes](https://github.com/actix/actix/releases)
- [Changelog](https://github.com/actix/actix/blob/master/CHANGES.md)
- [Commits](https://github.com/actix/actix/commits/v0.7.6)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
exonum/exonum,alekseysidorov/exonum,alekseysidorov/exonum,alekseysidorov/exonum,exonum/exonum,exonum/exonum,exonum/exonum,alekseysidorov/exonum