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

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-ACORN-559469

Author: snyk-bot

package-lock.json

@@ -43,7 +43,7 @@
     "tap": "^14.6.1"
   },
   "dependencies": {
-    "acorn": "5.7.1",
+    "acorn": "5.7.4",
     "debug": "^4.1.1",
     "needle": "^2.4.0",
     "semver": "^6.3.0",