Update juniper_rocket_async for the latest Rocket master (#905)

* Update for the latest Rocket master

* Run rustfmt

* Update tokio Version

* Improve Error Test Helper Function

* Improve Code Readability

Author: XiNiHa

juniper_rocket_async/Cargo.toml

@@ -16,7 +16,7 @@ futures = "0.3.1"
 juniper = { version = "0.15.3", path = "../juniper", default-features = false }
 rocket = { git = "https://github.com/SergioBenitez/Rocket", branch = "master", default-features = false }
 serde_json = "1.0.2"
-tokio = { version = "0.2", features = ["macros", "rt-core"] }
+tokio = { version = "1", features = ["macros", "rt"] }
 
 [dev-dependencies]
 juniper = { version = "0.15.3", path = "../juniper", features = ["expose-test-schema"] }