fix: cvat-core/package.json & cvat-core/package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-Y18N-1021887

cvat-core/package.json

@@ -39,7 +39,7 @@
     "detect-browser": "^5.2.0",
     "error-stack-parser": "^2.0.2",
     "form-data": "^2.5.0",
-    "jest-config": "^24.8.0",
+    "jest-config": "^26.0.0",
     "js-cookie": "^2.2.0",
     "jsonpath": "^1.0.2",
     "platform": "^1.3.5",