Update phf to 0.10

Author: Wu Yu Wei

Cargo.toml

@@ -24,7 +24,7 @@ cssparser-macros = {path = "./macros", version = "0.6"}
 dtoa-short = "0.3"
 itoa = "0.4"
 matches = "0.1"
-phf = {version = "0.8", features = ["macros"]}
+phf = {version = "0.10", features = ["macros"]}
 serde = {version = "1.0", optional = true}
 smallvec = "1.0"