fix: upgrade multiple dependencies with Snyk

Snyk has created this PR to upgrade:
  - gatsby-image from 2.4.14 to 2.4.20.
    See this package in npm: https://www.npmjs.com/package/gatsby-image
  - gatsby-plugin-emotion from 4.3.10 to 4.3.12.
    See this package in npm: https://www.npmjs.com/package/gatsby-plugin-emotion
  - gatsby-plugin-google-analytics from 2.3.13 to 2.3.15.
    See this package in npm: https://www.npmjs.com/package/gatsby-plugin-google-analytics
  - gatsby-plugin-google-tagmanager from 2.3.11 to 2.3.14.
    See this package in npm: https://www.npmjs.com/package/gatsby-plugin-google-tagmanager
  - gatsby-plugin-layout from 1.3.10 to 1.3.12.
    See this package in npm: https://www.npmjs.com/package/gatsby-plugin-layout
  - gatsby-plugin-manifest from 2.4.20 to 2.4.33.
    See this package in npm: https://www.npmjs.com/package/gatsby-plugin-manifest
  - gatsby-plugin-offline from 3.2.17 to 3.2.30.
    See this package in npm: https://www.npmjs.com/package/gatsby-plugin-offline
  - gatsby-plugin-react-helmet from 3.3.10 to 3.3.12.
    See this package in npm: https://www.npmjs.com/package/gatsby-plugin-react-helmet
  - gatsby-plugin-sitemap from 2.4.11 to 2.4.14.
    See this package in npm: https://www.npmjs.com/package/gatsby-plugin-sitemap
  - gatsby-remark-autolink-headers from 2.3.11 to 2.3.14.
    See this package in npm: https://www.npmjs.com/package/gatsby-remark-autolink-headers
  - gatsby-remark-images from 3.3.18 to 3.3.32.
    See this package in npm: https://www.npmjs.com/package/gatsby-remark-images
  - gatsby-source-filesystem from 2.3.21 to 2.3.32.
    See this package in npm: https://www.npmjs.com/package/gatsby-source-filesystem

See this project in Snyk:
https://app.snyk.io/org/github-newrelic/project/868cac7a-942a-4cb5-a87b-05381c8ca7ec?utm_source=github&utm_medium=upgrade-pr