Apollo Cache example: Allow maxAge to be 0

[Antti-Kaikkonen]

I used the CacheControl directive in my project, but it didn't allow me to set maxAge to 0.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (c8d2e2d) 95.50% compared to head (d2d9fb9) 95.50%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1608 +/- ## ======================================= Coverage 95.50% 95.50% ======================================= Files 113 113 Lines 1848 1848 Branches 364 364 ======================================= Hits 1765 1765 Misses 83 83 ```

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