[manifest] 6.1: Shortens manifest cache time in example (#427)

Replaces example of manifest being cached for one year with manifest being cached for 30 days.  

(In the world of apps, not having an update for one year seems like an unrealistic example.)
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/manifest/pull/427

-- Commit Summary --

  * 6.1: Shortens manifest cache time in example

-- File Changes --

    M index.html (4)

-- Patch Links --

https://github.com/w3c/manifest/pull/427.patch
https://github.com/w3c/manifest/pull/427.diff

---
Reply to this email directly or view it on GitHub:
https://github.com/w3c/manifest/pull/427