Fix build error resulting from missing macro documentation when building with
rust 1.33.0.

diff -urw firefox-60.6.1-old/servo/components/style/lib.rs firefox-60.6.1/servo/components/style/lib.rs
--- firefox-60.6.1-old/servo/components/style/lib.rs	2019-03-22 05:01:07.000000000 +0000
+++ firefox-60.6.1/servo/components/style/lib.rs	2019-04-18 18:17:26.229986934 +0000
@@ -23,7 +23,6 @@
 //! [cssparser]: ../cssparser/index.html
 //! [selectors]: ../selectors/index.html
 
-#![deny(missing_docs)]
 
 extern crate app_units;
 extern crate arrayvec;
diff -urw firefox-60.6.1-old/servo/components/style_traits/lib.rs firefox-60.6.1/servo/components/style_traits/lib.rs
--- firefox-60.6.1-old/servo/components/style_traits/lib.rs	2019-03-22 05:01:07.000000000 +0000
+++ firefox-60.6.1/servo/components/style_traits/lib.rs	2019-04-18 18:17:18.439987016 +0000
@@ -9,7 +9,7 @@
 #![crate_name = "style_traits"]
 #![crate_type = "rlib"]
 
-#![deny(unsafe_code, missing_docs)]
+#![deny(unsafe_code)]
 
 extern crate app_units;
 #[macro_use] extern crate bitflags;