fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-GATSBY-5671647
- https://snyk.io/vuln/SNYK-JS-GATSBYCLI-5671903
- https://snyk.io/vuln/SNYK-JS-GATSBYPLUGINSHARP-5671648
- https://snyk.io/vuln/SNYK-JS-GATSBYTRANSFORMERREMARK-5671901

Author: snyk-bot

package.json

@@ -6,7 +6,7 @@
   "dependencies": {
     "core-js": "^2.6.0",
     "disqus-react": "^1.0.4",
-    "gatsby": "^2.0.0",
+    "gatsby": "^5.0.0",
     "gatsby-image": "^2.0.22",
     "gatsby-link": "^2.0.7",
     "gatsby-plugin-canonical-urls": "^2.0.8",
@@ -15,13 +15,13 @@
     "gatsby-plugin-offline": "^2.0.5",
     "gatsby-plugin-react-helmet": "^3.0.0",
     "gatsby-plugin-sass": "^2.0.1",
-    "gatsby-plugin-sharp": "^2.0.15",
+    "gatsby-plugin-sharp": "^5.10.0",
     "gatsby-plugin-sitemap": "^2.0.3",
     "gatsby-plugin-yandex-metrika": "^1.0.5",
     "gatsby-remark-copy-linked-files": "^2.0.7",
     "gatsby-remark-images": "^3.0.1",
     "gatsby-source-filesystem": "^2.0.11",
-    "gatsby-transformer-remark": "^2.1.15",
+    "gatsby-transformer-remark": "^6.10.0",
     "gatsby-transformer-sharp": "^2.1.9",
     "lodash": "^4.17.4",
     "node-sass": "^4.9.3",