Impore OutputType from output area

src/notebook/notebook/nbformat.ts

@@ -3,7 +3,7 @@
 // https://github.com/jupyter/nbformat/blob/master/nbformat/v4/nbformat.v4.schema.json
 
 import {
-  MimeBundle
+  MimeBundle, OutputType
 } from '../output-area';
 
 
@@ -24,10 +24,6 @@ export
 const MINOR_VERSION = 0;
 
 
-export
-type OutputType = "execute_result" | "display_data" | "stream" | "error";
-
-
 export
 interface BaseOutput {
   output_type: OutputType;