Add prepare step to package.json

Author: grahamb

package.json

@@ -15,7 +15,8 @@
     "test": "nyc -r text-summary -r html mocha -r source-map-support/register -r ts-node/register './lib/**/*.spec.ts'",
     "build": "tsc",
     "lint": "eslint ./*.ts ./lib/**/*.ts",
-    "documentation": "typedoc"
+    "documentation": "typedoc",
+    "prepare": "npm run build"
   },
   "dependencies": {
     "cluster-key-slot": "1.1.0",