Add lint script to package.json

Author: elainefan331

package.json

@@ -50,7 +50,8 @@
     "start": "react-scripts start",
     "build": "react-scripts build",
     "test": "react-scripts test",
-    "eject": "react-scripts eject"
+    "eject": "react-scripts eject",
+    "lint": "eslint 'src/**/*.{js,jsx,ts,tsx}' --ext .js,.jsx,.ts,.tsx"
   },
   "browserslist": {
     "production": [