Swagger: fix definition of IPAM driver options

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

api/swagger.yaml

@@ -1484,11 +1484,9 @@ definitions:
             type: "string"
       Options:
         description: "Driver-specific options, specified as a map."
-        type: "array"
-        items:
-          type: "object"
-          additionalProperties:
-            type: "string"
+        type: "object"
+        additionalProperties:
+          type: "string"
 
   NetworkContainer:
     type: "object"