fix: docs/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-SHARP-5922108

docs/package.json

@@ -8,18 +8,18 @@
     "gatsby": "2.24.86",
     "gatsby-image": "2.4.13",
     "gatsby-plugin-i18n": "1.0.1",
-    "gatsby-plugin-manifest": "2.4.18",
+    "gatsby-plugin-manifest": "5.10.0",
     "gatsby-plugin-offline": "3.2.17",
     "gatsby-plugin-plausible": "0.0.7",
     "gatsby-plugin-react-helmet": "3.3.10",
-    "gatsby-plugin-sharp": "2.6.19",
+    "gatsby-plugin-sharp": "5.10.0",
     "gatsby-plugin-styled-components": "3.3.10",
     "gatsby-remark-check-links": "2.1.0",
     "gatsby-remark-images": "3.3.18",
     "gatsby-remark-prismjs": "3.5.10",
     "gatsby-source-filesystem": "2.3.19",
     "gatsby-transformer-remark": "2.8.25",
-    "gatsby-transformer-sharp": "2.5.11",
+    "gatsby-transformer-sharp": "5.10.0",
     "prismjs": "^1.25.0",
     "prop-types": "15.7.2",
     "react": "16.13.1",