add missing dep

Author: yyx990803

package.json

@@ -47,6 +47,7 @@
     "mocha": "^2.2.5",
     "node-libs-browser": "^0.5.2",
     "object-assign": "^3.0.0",
+    "postcss-selector-parser": "^1.1.2",
     "rimraf": "^2.4.0",
     "source-map": "^0.4.2",
     "style-loader": "^0.12.3",