Update euclid.

There are a few canvas2d-related dependencies that haven't updated, but they
only use euclid internally so that's not blocking landing the rest of the
changes.

Given the size of this patch, I think it's useful to get this landed as-is.

components/script_traits/webdriver_msg.rs

@@ -5,7 +5,7 @@
 #![allow(missing_docs)]
 
 use cookie::Cookie;
-use euclid::Rect;
+use euclid::default::Rect;
 use hyper_serde::Serde;
 use ipc_channel::ipc::IpcSender;
 use msg::constellation_msg::BrowsingContextId;