actually exclude test files from packaging

package.exclude takes glob syntax for determining what files to exclude
when excluding directories.

Fixes #169.

Author: froydnj

Cargo.toml

@@ -12,7 +12,7 @@ keywords = ["css", "syntax", "parser"]
 license = "MPL-2.0"
 build = "build.rs"
 
-exclude = ["src/css-parsing-tests"]
+exclude = ["src/css-parsing-tests/**"]
 
 [dev-dependencies]
 rustc-serialize = "0.3"