<enumeration description n> not display

My doc

``` markdown
## get sms code [POST /common/sms]

+ Request (application/json)

+ Attributes
+ type: `sign_in` (enum[string], required) - for the purposes of identity verification code
+ Members
+ `sign_in` - login
+ `sign_up` - sign up
+ `lost_password` - retrieve password
+ mobile: 13266668888 (string, required) - send verification code to the mobile
```

generated JSON Schema

``` json
{
"type": "object",
"properties": {
"type": {
"type": "string",
"enum": [
"signin",
"signup",
"lost_password"
],
"description": "for the purposes of identity verification code"
},
"mobile": {
"type": "string",
"description": "send verification code to the mobile"
}
},
"required": [
"type",
"mobile"
],
"$schema": "http://json-schema.org/draft-04/schema#"
}
```

Reference: [URI parameters section](https://github.com/apiaryio/api-blueprint/blob/master/API%20Blueprint%20Specification.md#uri-parameters-section)

Why not show enumeration description?

Start by reproducing the supplied API Blueprint example and comparing its generated JSON Schema with the URI parameters section of the API Blueprint Specification. Trace the renderer path for enum Members and their descriptions; done means the enumeration descriptions appear in the rendered documentation without breaking the existing schema output.

Written by the indexing model from the issue text.