Bump recursive-readdir (facebook#756)

Removes a deprecation warning:
npm WARN deprecated [email protected]: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue

See: jergason/recursive-readdir#39

Author: fson

Diff for: packages/react-scripts/package.json

@@ -58,7 +58,7 @@
     "postcss-loader": "0.13.0",
     "promise": "7.1.1",
     "react-dev-utils": "^0.2.0",
-    "recursive-readdir": "2.0.0",
+    "recursive-readdir": "2.1.0",
     "rimraf": "2.5.4",
     "strip-ansi": "3.0.1",
     "style-loader": "0.13.1",