fix: upgrade multiple dependencies with Snyk

Snyk has created this PR to upgrade:
  - gatsby from 2.23.1 to 2.23.3.
    See this package in NPM: https://www.npmjs.com/package/gatsby
  - gatsby-plugin-google-tagmanager from 2.3.4 to 2.3.5.
    See this package in NPM: https://www.npmjs.com/package/gatsby-plugin-google-tagmanager
  - gatsby-plugin-manifest from 2.4.10 to 2.4.11.
    See this package in NPM: https://www.npmjs.com/package/gatsby-plugin-manifest
  - gatsby-plugin-offline from 3.2.8 to 3.2.9.
    See this package in NPM: https://www.npmjs.com/package/gatsby-plugin-offline
  - gatsby-plugin-react-helmet from 3.3.3 to 3.3.4.
    See this package in NPM: https://www.npmjs.com/package/gatsby-plugin-react-helmet
  - gatsby-plugin-sass from 2.3.3 to 2.3.4.
    See this package in NPM: https://www.npmjs.com/package/gatsby-plugin-sass
  - gatsby-plugin-sitemap from 2.4.4 to 2.4.5.
    See this package in NPM: https://www.npmjs.com/package/gatsby-plugin-sitemap
  - gatsby-remark-images from 3.3.9 to 3.3.10.
    See this package in NPM: https://www.npmjs.com/package/gatsby-remark-images
  - gatsby-source-filesystem from 2.3.10 to 2.3.11.
    See this package in NPM: https://www.npmjs.com/package/gatsby-source-filesystem
  - gatsby-transformer-remark from 2.8.14 to 2.8.15.
    See this package in NPM: https://www.npmjs.com/package/gatsby-transformer-remark

See this project in Snyk:
https://app.snyk.io/org/github-newrelic/project/7fcca766-b226-4202-a6f2-d2d816b1e69d?utm_source=github&utm_medium=upgrade-pr