fix: package.json & yarn.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-SSRI-1085630

.gitignore

@@ -1,2 +1,3 @@
 node_modules
 .nuxt
+dist

package.json

@@ -27,7 +27,7 @@
     "graphql-tag": "^2.10.1",
     "moment": "^2.24.0",
     "node-sass": "^4.12.0",
-    "nuxt": "^2.8.1",
+    "nuxt": "^2.15.0",
     "nuxt-composition-api": "^0.9.3",
     "nuxt-i18n": "^6.0.1",
     "sass-loader": "^7.0.3",