fix: upgrade fetch-mock from 12.3.0 to 12.4.0

Snyk has created this PR to upgrade fetch-mock from 12.3.0 to 12.4.0.

See this package in npm:
fetch-mock

See this project in Snyk:
https://app.snyk.io/org/sunil-lakshman/project/c6925ec7-da6d-430a-a674-23c77f22d451?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot

package-lock.json

@@ -103,7 +103,7 @@
     "@contentstack/utils": "^1.3.15",
     "@fetch-mock/jest": "^0.2.10",
     "es6-promise": "^4.2.8",
-    "fetch-mock": "^12.2.0",
+    "fetch-mock": "^12.4.0",
     "localStorage": "1.0.4",
     "qs": "^6.14.0"
   }