Use shelljoin

Ensures any file arguments with spaces are correctly handled.

Author: pbrisbin

Diff for: lib/cc/engine/csslint.rb

@@ -62,7 +62,7 @@ def results
       end
 
       def csslint_xml
-        `csslint --format=checkstyle-xml #{files_to_inspect.join(" ")}`
+        `csslint --format=checkstyle-xml #{files_to_inspect.shelljoin}`
       end
 
       def files_to_inspect