chore(package): update should to version 13.0.0 (#13)

Author: greenkeeper[bot]

package.json

@@ -26,6 +26,6 @@
     "coveralls": "^2.11.2",
     "istanbul": "^0.4.5",
     "mocha": "^3.0.2",
-    "should": "^12.0.0"
+    "should": "^13.0.0"
   }
 }