Update post-processor.html.markdown

Fixed some typos in the interface{} mentions.

website/source/docs/extend/post-processor.html.markdown

@@ -46,11 +46,11 @@ type PostProcessor interface {
 
 The `Configure` method for each post-processor is called early in the
 build process to configure the post-processor. The configuration is passed
-in as a raw `interface{]`. The configure method is responsible for translating
+in as a raw `interface{}`. The configure method is responsible for translating
 this configuration into an internal structure, validating it, and returning
 any errors.
 
-For decoding the `interface{]` into a meaningful structure, the
+For decoding the `interface{}` into a meaningful structure, the
 [mapstructure](https://github.com/mitchellh/mapstructure) library is
 recommended. Mapstructure will take an `interface{}` and decode it into an
 arbitrarily complex struct. If there are any errors, it generates very