Update Idle.vue

[nadilas]

fixes missing computed property

[gabrielstuff]

Hello, Thanks for your contribution.

As we might remove this part of the code in the next idle-vue release, I'm not sure if I will merge this changes.

Will mark it, in order to not forget to add it on the idle-vue-display component which will use idle-vue under the hood.

Thanks !

[nadilas]

No problem, just wanted to let you know. :-)