Format IID as uppercase in GraphQL style guide

doc/development/api_graphql_styleguide.md

@@ -611,7 +611,7 @@ descriptions:
 Example:
 
 ```ruby
-field :id, GraphQL::ID_TYPE, description: 'ID of the Issue'
+field :id, GraphQL::ID_TYPE, description: 'ID of the issue'
 field :confidential, GraphQL::BOOLEAN_TYPE, description: 'Indicates the issue is confidential'
 field :closed_at, Types::TimeType, description: 'Timestamp of when the issue was closed'
 ```
@@ -1190,7 +1190,7 @@ argument :project_path, GraphQL::ID_TYPE,
 
 argument :iid, GraphQL::STRING_TYPE,
          required: true,
-         description: "The iid of the merge request to mutate"
+         description: "The IID of the merge request to mutate"
 
 argument :wip,
          GraphQL::BOOLEAN_TYPE,