fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:tunnel-agent:20170305

Latest report for riyadhalnur/node-base64-image:
https://snyk.io/test/github/riyadhalnur/node-base64-image

package.json

@@ -70,6 +70,6 @@
   "dependencies": {
     "lodash": "4.11.1",
     "polygoat": "1.1.4",
-    "request": "2.74.0"
+    "request": "2.81.0"
   }
 }