Merge pull request #29 from codeclimate/jp/add-performance-category

Add Performance category

Author: mrb

SPEC.md

@@ -98,6 +98,7 @@ Issues must be associated with one or more categories. Valid issue `categories`
 - `Compatibility` -- TODO describe me
 - `Complexity` -- TODO describe me
 - `Duplication` -- TODO describe me
+- `Performance` -- TODO describe me
 - `Security` -- TODO describe me
 - `Style` -- TODO describe me