chore(package): update should to version 13.1.0

Closes #152

Author: greenkeeper[bot]

package.json

@@ -44,7 +44,7 @@
     "mocha": "3.5.3",
     "phantomjs-prebuilt": "2.1.15",
     "semver": "5.4.1",
-    "should": "12.0.0",
+    "should": "13.1.0",
     "ts-loader": "2.3.7",
     "tslib": "1.7.1",
     "tslint": "5.7.0",