fix: Use 'json' as language name when parsing chart block from file (#173)

Author: OlegWock

src/notebooks/deepnote/converters/visualizationBlockConverter.ts

@@ -84,7 +84,7 @@ export class VisualizationBlockConverter implements BlockConverter {
         };
 
         const jsonContent = JSON.stringify(config, null, 2);
-        const cell = new NotebookCellData(NotebookCellKind.Code, jsonContent, 'JSON');
+        const cell = new NotebookCellData(NotebookCellKind.Code, jsonContent, 'json');
 
         return cell;
     }

src/notebooks/deepnote/converters/visualizationBlockConverter.unit.test.ts

@@ -59,7 +59,7 @@ suite('VisualizationBlockConverter', () => {
             const cell = converter.convertToCell(block);
 
             assert.strictEqual(cell.kind, NotebookCellKind.Code);
-            assert.strictEqual(cell.languageId, 'JSON');
+            assert.strictEqual(cell.languageId, 'json');
             assert.include(cell.value, '\n');
             assert.match(cell.value, /{\n  "variable"/);