add cache for mac-model

[psychopasss]

When the network is poor, it's slow

[alanhe421]

1. Thank you.
2. Here I need to make some modifications, the cache data should stored in alfred_workflow_cache.In this way, the cached data will not be carried when exporting the workflow.
3. I will deal with it in two days, or suggest you to modify it directly.

[alanhe421]

I made some modifications. I save cache data to alfred_workflow_cache.

the final version is

https://github.com/alanhg/alfred-workflows/blob/master/about-mac/src/mac-model-year.sh

[alanhe421]

Added contributors list to thank you for your contributions.

see https://github.com/alanhg/alfred-workflows#contributors