Quote delimited, comma separated strings are not supported.

Related issue:
babel/website#2436

Author: ryanpcmcquen

package.json

@@ -7,7 +7,7 @@
     "type-check:watch": "npm run type-check -- --watch",
     "build": "npm run build:types && npm run build:js",
     "build:types": "tsc --emitDeclarationOnly",
-    "build:js": "babel src --out-dir lib --extensions \".ts,.tsx\" --source-maps inline"
+    "build:js": "babel src --out-dir lib --extensions .ts,.tsx --source-maps inline"
   },
   "devDependencies": {
     "@babel/cli": "^7.8.3",