Add tslib as a dependency explicitly

Author: EmilianoSanchez

package-lock.json

@@ -66,6 +66,7 @@
   "dependencies": {
     "@splitsoftware/splitio-commons": "1.13.1",
     "@types/google.analytics": "0.0.40",
+    "tslib": "^2.3.1",
     "unfetch": "^4.2.0"
   },
   "devDependencies": {