Bug 1607697 - Allow excessive precision in debug color constants. r=Gankro

Addresses a clippy lint.

Differential Revision: https://phabricator.services.mozilla.com/D59113

--HG--
extra : moz-landing-system : lando

gfx/wr/webrender/src/debug_colors.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #![allow(dead_code)]
+#![cfg_attr(feature = "cargo-clippy", allow(clippy::excessive_precision))]
 
 use api::ColorF;