build: upgrade types of eslint

Author: tyankatsu0105

package.json

@@ -60,7 +60,7 @@
     "vue-eslint-parser": "^7.1.0"
   },
   "devDependencies": {
-    "@types/eslint": "^6.8.1",
+    "@types/eslint": "^7.2.0",
     "@types/natural-compare": "^1.4.0",
     "@types/node": "^13.13.5",
     "@typescript-eslint/parser": "^3.0.2",