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

The following vulnerabilities are fixed with a Snyk patch:
- https://snyk.io/vuln/SNYK-JS-LODASH-450202

.snyk

@@ -0,0 +1,18 @@
+# Snyk (https://snyk.io) policy file, patches or ignores known vulnerabilities.
+version: v1.13.5
+ignore: {}
+# patches apply the minimum changes required to fix a vulnerability
+patch:
+  SNYK-JS-LODASH-450202:
+    - async > lodash:
+        patched: '2019-07-04T00:57:48.910Z'
+    - Arsenal > async > lodash:
+        patched: '2019-07-04T00:57:48.910Z'
+    - Arsenal > ioredis > lodash:
+        patched: '2019-07-04T00:57:48.910Z'
+    - vaultclient > Arsenal > async > lodash:
+        patched: '2019-07-04T00:57:48.910Z'
+    - vaultclient > Arsenal > ioredis > lodash:
+        patched: '2019-07-04T00:57:48.910Z'
+    - vaultclient > xml2js > xmlbuilder > lodash:
+        patched: '2019-07-04T00:57:48.910Z'

package.json

@@ -22,7 +22,8 @@
     "ioredis": "^4.9.5",
     "node-schedule": "1.2.0",
     "vaultclient": "scality/vaultclient#fbd9988d",
-    "werelogs": "scality/werelogs#0ff7ec82"
+    "werelogs": "scality/werelogs#0ff7ec82",
+    "snyk": "^1.189.0"
   },
   "devDependencies": {
     "aws4": "^1.8.0",
@@ -38,6 +39,9 @@
     "lint": "eslint $(git ls-files '*.js')",
     "lint_md": "mdlint $(git ls-files '*.md')",
     "start": "node server.js",
-    "test": "mocha --recursive tests/unit"
-  }
+    "test": "mocha --recursive tests/unit",
+    "snyk-protect": "snyk protect",
+    "prepare": "npm run snyk-protect"
+  },
+  "snyk": true
 }