fix(package): update zone.js to version 0.8.18 (#259)

Author: greenkeeper[bot]

package.json

@@ -69,6 +69,6 @@
     "utf-8-validate": "^3.0.3",
     "winston": "^2.3.1",
     "xterm": "^2.8.1",
-    "zone.js": "0.8.17"
+    "zone.js": "0.8.18"
   }
 }