Update actix requirement from 0.12 to 0.13

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

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

juniper_actix/Cargo.toml

@@ -12,7 +12,7 @@ repository = "https://github.com/graphql-rust/juniper"
 subscriptions = ["juniper_graphql_ws", "tokio"]
 
 [dependencies]
-actix = "0.12"
+actix = "0.13"
 actix-http = "3.0.0-beta.15"
 http = "0.2.4"
 actix-web = "4.0.0-beta.14"