fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-LODASH-1018905
- https://snyk.io/vuln/SNYK-JS-LODASH-1040724

Author: snyk-bot

package.json

@@ -23,7 +23,7 @@
 		"documentation": "^13.2.0",
 		"fs-extra": "^7.0.1",
 		"gatsby": "^2.32.11",
-		"gatsby-plugin-advanced-sitemap": "^1.6.0",
+		"gatsby-plugin-advanced-sitemap": "^2.0.0",
 		"gatsby-plugin-react-helmet": "^3.3.3",
 		"gatsby-plugin-sass": "^2.8.0",
 		"gatsby-plugin-sharp": "^3.1.2",