Update phf requirement from 0.8 to 0.9

Updates the requirements on [phf](https://github.com/sfackler/rust-phf) to permit the latest version.
- [Release notes](https://github.com/sfackler/rust-phf/releases)
- [Changelog](https://github.com/rust-phf/rust-phf/blob/master/CHANGELOG.md)
- [Commits](rust-phf/rust-phf@v0.8.0...v0.9.0)

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

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

Author: dependabot[bot]

bui-demo/Cargo.toml

@@ -14,7 +14,7 @@ bui-backend-types = {version="0.8", path="../types", features=["uuid-v4"]}
 log = "0.4"
 env_logger = "0.9"
 includedir = {version="0.6", optional=true}
-phf = {version="0.8", optional=true}
+phf = {version="0.9", optional=true}
 serde = "1.0"
 serde_json = "1.0"
 clap = "2.20.0"