fix "not valid as a React child" error while display crds with column which type is object (#1772)

Signed-off-by: liuhongyu <lhy990409@gmail.com>

src/renderer/components/+custom-resources/crd-resources.tsx

@@ -93,7 +93,7 @@ export class CrdResources extends React.Component<Props> {
           isNamespaced && crdInstance.getNs(),
           ...extraColumns.map(column => ({
             renderBoolean: true,
-            children: jsonPath.value(crdInstance, column.jsonPath.slice(1)),
+            children: JSON.stringify(jsonPath.value(crdInstance, column.jsonPath.slice(1))),
           })),
           crdInstance.getAge(),
         ]}