Fix theme zipping in Docker (#38)

- Default to port 80

src/MyWebLog/appsettings.json

@@ -4,5 +4,12 @@
     "LogLevel": {
       "MyWebLog.Handlers": "Information"
     }
+  },
+  "Kestrel": {
+    "Endpoints": {
+      "Http": {
+        "Url": "http://0.0.0.0:80"
+      }
+    }
   }
 }