Themes: add minzoom to ski_piste and aerialway, fix #1876

assets/layers/aerialway/aerialway.json

@@ -8,6 +8,7 @@
     "en": "Various forms of transport for passengers and goods that use wires, including cable cars, gondolas, chair lifts, drag lifts, and zip lines. ",
     "de": "Alle Arten von seil- oder drahtgestütztem Personen- oder Gütertransport, wie Seilbahnen, Gondeln, Sessellifte, Schlepplifte. "
   },
+  "minzoom": 11,
   "source": {
     "osmTags": {
       "and": [

assets/layers/ski_piste/ski_piste.json

@@ -8,6 +8,7 @@
     "en": "Ski and snowboard pistes",
     "de": "Ski- und Snowboardpisten"
   },
+  "minzoom": 11,
   "source": {
     "osmTags": {
       "and": [