Merge pull request #1904 from lqd/htlm5ever-broken

allow soft-unstable on stable `html5ever` benchmark

Author: Mark-Simulacrum

collector/compile-benchmarks/html5ever/build.rs

@@ -7,6 +7,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![allow(soft_unstable)]
+
 extern crate phf_codegen;
 extern crate rustc_serialize;