Bump rustc_demangle version

lu-zero · lu-zero · commit d1ba68a92add · 2018-05-17T15:52:49.000Z
Otherwise some objdump output would not parse correctly.
diff --git a/crates/stdsimd-test/Cargo.toml b/crates/stdsimd-test/Cargo.toml
@@ -9,4 +9,4 @@ simd-test-macro = { path = "../simd-test-macro" }
 backtrace = "0.3"
 cc = "1.0"
 lazy_static = "0.2"
-rustc-demangle = "0.1"
+rustc-demangle = "0.1.8"
