Remove no_std category (crates.io doesn't support it, and it is now rejected), use keywords instead

Author: Manishearth

idna/Cargo.toml

@@ -3,7 +3,7 @@ name = "idna"
 version = "1.0.2"
 authors = ["The rust-url developers"]
 description = "IDNA (Internationalizing Domain Names in Applications) and Punycode."
-categories = ["no_std"]
+keywords = ["no_std", "web", "http"]
 repository = "https://github.com/servo/rust-url/"
 license = "MIT OR Apache-2.0"
 autotests = false