add icons to gatsby-config.js

[frames75]

Building the frontend, when you do:

$ cd frontend
$ npm install
$ npm run develop

This last command returns next error:

> gatsby-starter-default@0.1.0 develop /home/carpanta/Documentos/Cosas/Curro/nodejs/strapi/temp-pullreq-strapi-starte/strapi-starter-gatsby-blog/frontend
> gatsby develop

success open and validate gatsby-configs - 0.064s

 ERROR #11331  PLUGIN

Invalid plugin options for "gatsby-plugin-manifest":

- "value" must contain at least one of [icon, icons]

not finished load plugins - 0.687s

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! gatsby-starter-default@0.1.0 develop: `gatsby develop`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the gatsby-starter-default@0.1.0 develop script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/carpanta/.npm/_logs/2020-12-21T16_12_06_775Z-debug.log

The Error is solved by adding to frontend/gatsby-config.js the properties icon and icons.

It's not necessary to add the icons files.

---

Linux Mint 19.2 Strapi: v3.4.0 Node.js: v14.15.3

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