Update actix-web requirement from =0.7.12 to =0.7.13 (exonum#1008)

Updates the requirements on [actix-web](https://github.com/actix/actix-web) to permit the latest version.
- [Release notes](https://github.com/actix/actix-web/releases)
- [Changelog](https://github.com/actix/actix-web/blob/master/CHANGES.md)
- [Commits](https://github.com/actix/actix-web/commits/v0.7.13)

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

exonum/Cargo.toml

@@ -19,7 +19,7 @@ circle-ci = { repository = "exonum/exonum" }
 [dependencies]
 actix = "=0.7.5"
 actix-net = "=0.1.1"
-actix-web = "=0.7.12"
+actix-web = "=0.7.13"
 log = "=0.4.5"
 byteorder = "1.2.3"
 hex = "=0.3.2"

testkit/Cargo.toml

@@ -19,7 +19,7 @@ travis-ci = { repository = "exonum/exonum" }
 circle-ci = { repository = "exonum/exonum" }
 
 [dependencies]
-actix-web = "=0.7.12"
+actix-web = "=0.7.13"
 exonum = { version = "0.9.0", path = "../exonum" }
 failure = "0.1.2"
 futures = "=0.1.25"