Temperature unit selects: use lower case in icons.json also

Issue #1579

custom_components/tuya_local/icons.json

@@ -20,7 +20,7 @@
             "temperature_unit": {
                 "default": "mdi:temperature-celsius",
                 "state": {
-                    "Fahrenheit": "mdi:temperature-fahrenheit"
+                    "fahrenheit": "mdi:temperature-fahrenheit"
                 }
             }
         }