add keyword-spacing rule (#8)

Ref: http://eslint.org/docs/rules/keyword-spacing
Saves us time in reviews (avoids nit comments)

lib/configs/default.js

@@ -24,6 +24,7 @@ module.exports = {
     'handle-callback-err': 1,
     'indent': [2, 2], // 2 spaces indentation
     'key-spacing': 0,
+    'keyword-spacing': 2,
     'new-cap': 0,
     'no-cond-assign': [2, 'except-parens'],
     'no-debugger': 2,