docs(ability): fixes confusing ability check for Post.price

Fixes #242

docs/_posts/2017-07-21-check-abilities.md

@@ -61,20 +61,20 @@ const ability = AbilityBuidler.define((can, cannot) => {
   }
 })
 
-ability.throwUnlessCan('update', 'Post', 'price')
+ability.throwUnlessCan('update', 'Product', 'price')
 ```
 
 The code above will throw error with corresponding message, if user is not an admin.
 Also that error object contains information about what `action`, `subject` and `field` were checked, so you can use this to provide template message and evaluate it later:
 
 ```js
 try {
-  ability.throwUnlessCan('update', 'Post', 'price')
+  ability.throwUnlessCan('update', 'Product', 'price')
 } catch (error) {
   console.log(error.message) // "Only admins can update product prices"
   console.log(error.action) // "update"
-  console.log(error.subjectName) // "Post"
-  console.log(error.subject) // "Post", does not equal `subjectName` when check on instance
+  console.log(error.subjectName) // "Product"
+  console.log(error.subject) // "Product", does not equal `subjectName` when check on instance
 }
 ```