feat(deps): update superagent to ^6.1.0 (#281)

Bump `superagent` to ^6.1.0 to fix security vulnerabilities.

BREAKING CHANGE: upgrades superagent to a new major version, closes #265

Author: Exotrom

package-lock.json

@@ -51,13 +51,13 @@
   },
   "dependencies": {
     "@types/chai": "4",
-    "@types/superagent": "^3.8.3",
+    "@types/superagent": "^4.1.10",
     "charset": "^1.0.1",
-    "cookiejar": "^2.1.1",
+    "cookiejar": "^2.1.2",
     "is-ip": "^2.0.0",
     "methods": "^1.1.2",
     "qs": "^6.5.1",
-    "superagent": "^3.7.0"
+    "superagent": "^6.1.0"
   },
   "devDependencies": {
     "@semantic-release/changelog": "^3.0.2",