deps: update ESLint version to v6.4.0

BREAKING CHANGE: drop support for ESLint less than v6.4.0

Author: koba04

package.json

@@ -28,15 +28,15 @@
   "license": "MIT",
   "devDependencies": {
     "@types/react": "^16.9.9",
-    "eslint": "^6.3.0",
+    "eslint": "^6.4.0",
     "mocha": "^6.2.1",
     "npm-run-all": "^4.1.5",
     "prettier": "^1.18.2",
     "standard-version": "^7.0.0",
     "typescript": "^3.6.4"
   },
   "peerDependencies": {
-    "eslint": "^6.0.0",
+    "eslint": "^6.4.0",
     "typescript": "^3.3.3333"
   },
   "dependencies": {