feat(package): use node-postal module compatible with node12

This updates our dependencies to use the Node.js 12 (and 10) compatible
fork of [node-postal](https://github.com/openvenues/node-postal).

The fork is located at [imothee/node-postal](https://github.com/imothee/node-postal).

Connects pelias/pelias#800

package.json

@@ -34,7 +34,7 @@
     "jsftp": "^2.0.0",
     "lodash": "^4.17.4",
     "morgan": "^1.9.0",
-    "node-postal": "^1.0.0",
+    "node-postal": "imothee/node-postal#6d0b00f68a",
     "pbf2json": "^6.4.0",
     "pelias-config": "^4.0.0",
     "pelias-logger": "^1.2.1",