fix: .snyk & package.json to reduce vulnerabilities

The following vulnerabilities are fixed with a Snyk patch:
- https://snyk.io/vuln/npm:hoek:20180212

.snyk

@@ -0,0 +1,22 @@
+# Snyk (https://snyk.io) policy file, patches or ignores known vulnerabilities.
+version: v1.12.0
+ignore: {}
+# patches apply the minimum changes required to fix a vulnerability
+patch:
+  'npm:hoek:20180212':
+    - mapnik > node-pre-gyp > hawk > hoek:
+        patched: '2018-06-20T03:22:06.695Z'
+    - mapnik > node-pre-gyp > hawk > boom > hoek:
+        patched: '2018-06-20T03:22:06.695Z'
+    - mapnik > node-pre-gyp > hawk > sntp > hoek:
+        patched: '2018-06-20T03:22:06.695Z'
+    - mapnik > node-pre-gyp > hawk > cryptiles > boom > hoek:
+        patched: '2018-06-20T03:22:06.695Z'
+    - mapnik > node-pre-gyp > request > hawk > hoek:
+        patched: '2018-06-20T03:22:06.695Z'
+    - mapnik > node-pre-gyp > request > hawk > boom > hoek:
+        patched: '2018-06-20T03:22:06.695Z'
+    - mapnik > node-pre-gyp > request > hawk > sntp > hoek:
+        patched: '2018-06-20T03:22:06.695Z'
+    - mapnik > node-pre-gyp > request > hawk > cryptiles > boom > hoek:
+        patched: '2018-06-20T03:22:06.695Z'

package.json

@@ -23,7 +23,9 @@
     "lint": "eslint src test",
     "test": "node test/index.js",
     "cz": "git-cz",
-    "release": "standard-version"
+    "release": "standard-version",
+    "snyk-protect": "snyk protect",
+    "prepare": "npm run snyk-protect"
   },
   "config": {
     "commitizen": {
@@ -32,7 +34,8 @@
   },
   "dependencies": {
     "mapnik": "^3.7.2",
-    "mapnik-pool": "^0.1.3"
+    "mapnik-pool": "^0.1.3",
+    "snyk": "^1.83.0"
   },
   "devDependencies": {
     "@mapbox/tilelive": "^6.0.0",
@@ -43,5 +46,6 @@
     "eslint-plugin-import": "^2.12.0",
     "standard-version": "^4.4.0",
     "tape": "^4.9.1"
-  }
+  },
+  "snyk": true
 }