feat(docker): add download script separate from npm

For the same reasons we need to avoid calling `npm start` in Docker
containers, we need to avoid calling `npm run download`.

By moving the knowledge of how to do a download from `package.json` to a small
script, Docker containers can work without any NPM interference while still
having consistency. `npm run download` can call this script for backwards
compatibility and convenience when running outside Docker.

Connects pelias/pelias#745

bin/download

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+exec node utils/download_data.js

package.json

@@ -38,7 +38,7 @@
     "temp": "^0.8.3"
   },
   "scripts": {
-    "download": "node utils/download_data.js",
+    "download": "./bin/download",
     "import": "./bin/start",
     "parallel": "./bin/parallel",
     "test": "NODE_ENV=test npm run units",