fix: package.json & package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-JSZIP-1251497

Author: snyk-bot

package-lock.json

@@ -32,7 +32,7 @@
   },
   "dependencies": {
     "file-saver": "^1.3.8",
-    "jszip": "^3.0.0"
+    "jszip": "^3.7.0"
   },
   "devDependencies": {
     "babel-core": "^6.26.3",