Update warp requirement from 0.3.2 to 0.4.0

Updates the requirements on [warp](https://github.com/seanmonstar/warp) to permit the latest version.
- [Release notes](https://github.com/seanmonstar/warp/releases)
- [Changelog](https://github.com/seanmonstar/warp/blob/master/CHANGELOG.md)
- [Commits](seanmonstar/warp@v0.3.2...v0.4.0)

---
updated-dependencies:
- dependency-name: warp
  dependency-version: 0.4.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

juniper_warp/Cargo.toml

@@ -38,7 +38,7 @@ juniper_graphql_ws = { version = "0.4.0", path = "../juniper_graphql_ws", featur
 log = { version = "0.4", optional = true }
 serde_json = "1.0.18"
 tokio = { version = "1.0", features = ["rt"] }
-warp = { version = "0.3.2", default-features = false }
+warp = { version = "0.4.0", default-features = false }
 
 # Fixes for `minimal-versions` check.
 # TODO: Try remove on upgrade of `warp` crate.