Add classnames as devDependencies

Author: cheton

package.json

@@ -53,6 +53,7 @@
     "babel-preset-es2015": "^6.6.0",
     "babel-preset-react": "^6.5.0",
     "babel-preset-stage-0": "^6.5.0",
+    "classnames": "^2.2.5",
     "coveralls": "^2.11.9",
     "css-loader": "^0.23.1",
     "eslint": "^2.7.0",