Add failing test case for one postcode deduping

test/unit/fixture/dedupe_only_postalcode_differs.js

@@ -0,0 +1,27 @@
+module.exports = [
+  {
+    '_id': '101914069',
+    'layer': 'venue',
+    'source': 'openstreetmap',
+    'name': {
+      'default': 'A place'
+    },
+    'parent': {
+      'country_a': ['USA']
+    }
+  },
+  {
+    '_id': '323',
+    'layer': 'venue',
+    'source': 'openstreetmap',
+    'name': {
+      'default': 'A place'
+    },
+    'address_parts': {
+      'zip': '97005'
+    },
+    'parent': {
+      'country_a': ['USA']
+    }
+  }
+];