chore(package): update tslib to version 1.8.1

Author: greenkeeper[bot]

package.json

@@ -45,7 +45,7 @@
     "semver": "5.4.1",
     "should": "13.1.1",
     "ts-loader": "3.2.0",
-    "tslib": "1.8.0",
+    "tslib": "1.8.1",
     "tslint": "5.7.0",
     "tslint-loader": "3.5.3",
     "typedoc": "0.9.0",