Bump version to 0.8.5

This will allow dependent packages to pick up improvements to mutex
performance.

Author: mrobinson

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "string_cache"
-version = "0.8.4"  # Also update README.md when making a semver-breaking change
+version = "0.8.5"  # Also update README.md when making a semver-breaking change
 authors = [ "The Servo Project Developers" ]
 description = "A string interning library for Rust, developed as part of the Servo project."
 license = "MIT OR Apache-2.0"