feat: add ESLint 6 to peerDeps

Author: kazupon

package.json

@@ -14,7 +14,7 @@
   },
   "homepage": "https://github.com/vuejs/eslint-plugin-vue-libs#readme",
   "peerDependencies": {
-    "eslint": "^5.11.1"
+    "eslint": "^5.11.1 || ^6.0.0"
   },
   "dependencies": {
     "babel-eslint": "^10.0.1",