[react-pacakger] Fix failing test

Summary:
Fix failing test that matches the exact error string to match using `contains`.

I was under the impression that jest tests were running in CI -- turns out not yet.

react-packager/src/SocketInterface/__tests__/SocketClient-test.js

@@ -107,6 +107,6 @@ describe('SocketClient', () => {
       data: 'some error'
     });
 
-    return promise.catch(m => expect(m.message).toBe('some error'));
+    return promise.catch(m => expect(m.message).toContain('some error'));
   });
 });