make component unit test for component/panel/row.js

[hideokamoto]

Description

Related to progress on the issue -> Unit Testing Components #641

Added some unit test scripts for PanelRow component.

How Has This Been Tested?

Run unit test command.

$ npm run test-unit
 PASS  components/panel/test/row.js
  PanelRow
    ✓ should defined default class name (18ms)
    ✓ should defined custom class name (4ms)
    ✓ should return child components (8ms)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows has proper inline documentation.

[youknowriad]

Thanks for the unit test. Looks good to me