Add version to docs and object casting to command prep

docs/includes/apiargs-MongoDBCollection-method-aggregate-option.yaml

@@ -34,9 +34,18 @@ post: |
   Document validation requires MongoDB 3.2 or later: if you are using an earlier
   version of MongoDB, this option will be ignored.
 ---
-source:
-  file: apiargs-MongoDBCollection-method-find-option.yaml
-  ref: hint
+arg_name: option
+name: hint
+type: string|array|object
+description: |
+  The index to use. Specify either the index name as a string or the index key
+  pattern as a document. If specified, then the query system will only consider
+  plans using the hinted index.
+
+  .. versionadded:: 1.3
+interface: phpmethod
+operation: ~
+optional: true
 ---
 source:
   file: apiargs-common-option.yaml

src/Operation/Aggregate.php

@@ -281,7 +281,7 @@ class Aggregate implements Executable
         }
 
         if (isset($this->options['hint'])) {
-            $cmd['hint'] = $this->options['hint'];
+            $cmd['hint'] = is_array($this->options['hint']) ? (object) $this->options['hint'] : $this->options['hint'];
         }
 
         if (isset($this->options['maxTimeMS'])) {