feat: add the ability to run with '--json' and output the result (#78)

* addition-of-json-flag

* Set output of npn audit

__tests__/testdata/audit/error.json

@@ -0,0 +1,73 @@
+{
+  "actions": [
+    {
+      "isMajor": false,
+      "action": "install",
+      "resolves": [
+        {
+          "id": 532,
+          "path": "moment",
+          "dev": false,
+          "optional": false,
+          "bundled": false
+        }
+      ],
+      "module": "moment",
+      "target": "2.29.1"
+    }
+  ],
+  "advisories": {
+    "532": {
+      "findings": [
+        {
+          "version": "2.19.2",
+          "paths": [
+            "moment"
+          ]
+        }
+      ],
+      "id": 532,
+      "created": "2017-09-21T20:40:00.889Z",
+      "updated": "2019-06-24T15:10:05.868Z",
+      "deleted": null,
+      "title": "Regular Expression Denial of Service",
+      "found_by": {
+        "name": "Cristian-Alexandru Staicu"
+      },
+      "reported_by": {
+        "name": "Cristian-Alexandru Staicu"
+      },
+      "module_name": "moment",
+      "cves": [],
+      "vulnerable_versions": "<2.19.3",
+      "patched_versions": ">=2.19.3",
+      "overview": "Affected versions of `moment` are vulnerable to a low severity regular expression denial of service when parsing dates as strings.",
+      "recommendation": "Update to version 2.19.3 or later.",
+      "references": "- [Issue #4163](https://github.com/moment/moment/issues/4163)\n- [PR #4326](https://github.com/moment/moment/pull/4326)",
+      "access": "public",
+      "severity": "low",
+      "cwe": "CWE-400",
+      "metadata": {
+        "module_type": "",
+        "exploitability": 5,
+        "affected_components": ""
+      },
+      "url": "https://npmjs.com/advisories/532"
+    }
+  },
+  "muted": [],
+  "metadata": {
+    "vulnerabilities": {
+      "info": 0,
+      "low": 7,
+      "moderate": 1,
+      "high": 5,
+      "critical": 0
+    },
+    "dependencies": 659,
+    "devDependencies": 0,
+    "optionalDependencies": 0,
+    "totalDependencies": 659
+  },
+  "runId": "88c86b12-b4a4-4827-9d3c-d58ae74384c5"
+}