Fixed js-yaml version in package-lock.json. Security vulnerability.

package-lock.json

 {
   "name": "jsmodbus",
-  "version": "3.1.2",
+  "version": "3.1.7",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
@@ -981,9 +981,9 @@
       "dev": true
     },
     "js-yaml": {
-      "version": "3.12.1",
-      "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-3.12.1.tgz",
-      "integrity": "sha512-um46hB9wNOKlwkHgiuyEVAybXBjwFUV0Z/RaHJblRd9DXltue9FTYvzCr9ErQrK9Adz5MU4gHWVaNUfdmrC8qA==",
+      "version": "3.13.1",
+      "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-3.13.1.tgz",
+      "integrity": "sha512-YfbcO7jXDdyj0DGxYVSlSeQNHbD7XPWvrVWeVUujrQEoZzWJIRrCPoyk6kL6IAjAG2IolMK4T0hNUe0HOUs5Jw==",
       "dev": true,
       "requires": {
         "argparse": "^1.0.7",

package.json

 {
   "name": "jsmodbus",
-  "version": "3.1.6",
+  "version": "3.1.7",
   "description": "Implementation for the Serial/TCP Modbus protocol.",
   "author": "Stefan Poeter <stefan.poeter@cloud-automation.de>",
   "main": "./src/modbus.js",