added eslint-watch.

Author: takaokouji

package.json

@@ -57,6 +57,7 @@
     "eslint-config-scratch": "^5.0.0",
     "eslint-plugin-import": "^2.8.0",
     "eslint-plugin-react": "^7.5.1",
+    "eslint-watch": "^4.0.2",
     "file-loader": "2.0.0",
     "get-float-time-domain-data": "0.1.0",
     "get-user-media-promise": "1.1.4",