Add unclassified highways to Sidewalks theme

In the hierarchy, unclassified highways are between residential and tertiary / secondary, which are already considered in the theme.

assets/themes/sidewalks/sidewalks.json

@@ -32,6 +32,7 @@
         "osmTags": {
           "or": [
             "highway=residential",
+            "highway=unclassified",
             "highway=tertiary",
             "highway=secondary"
           ]
@@ -177,4 +178,4 @@
       "allowSplit": true
     }
   ]
-}
+}