fix: .snyk & package.json to reduce vulnerabilities

The following vulnerabilities are fixed with a Snyk patch:
- https://snyk.io/vuln/SNYK-JS-TREEKILL-536781

package.json

@@ -23,7 +23,7 @@
     "nuxt": "^2.0.0",
     "s-ago": "^1.3.0",
     "sass-loader": "^7.0.3",
-    "snyk": "^1.231.0",
+    "snyk": "^1.258.2",
     "vue": "^2.5.22",
     "vue-lazyload": "^1.2.6",
     "vue-numeral-filter": "^1.1.1",
@@ -41,7 +41,7 @@
     "test:cypress": "cypress run",
     "wait": "wait-on http://localhost:3000",
     "snyk-protect": "snyk protect",
-    "prepublish": "npm run snyk-protect"
+    "prepublish": "yarn run snyk-protect"
   },
   "devDependencies": {
     "@nuxtjs/vuetify": "^1.9.0",