Add rollup in devdep

Author: znck

package.json

@@ -52,7 +52,7 @@
     "istanbul": "^0.4.2",
     "mocha": "^2.3.4",
     "mocha-lcov-reporter": "^1.0.0",
-    "rollup": "latest",
+    "rollup": "^0.35.7",
     "rollup-plugin-buble": "^0.13.0",
     "rollup-plugin-replace": "latest",
     "stylus": "^0.54.5",