fix(blog)Update 100DaysOfGatsby challenge 7 description (#21436)
fix(blog)Update 100DaysOfGatsby challenge 7 description (#21436)

* Update excerpt to correct description

* Update docs/blog/100days/pwa/index.md

Co-Authored-By: LB <215e3d7c445b99629add69586ce9b88253e8211e@gmail.com>

Co-authored-by: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>
Co-authored-by: GatsbyJS Bot <313a651c59fdaade90d152972001707d94b0975c@gmail.com>

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