fix: correctly check if the proxy setting evaluates to false (#1336)

src/lib/up-storage.js

@@ -551,7 +551,7 @@ class ProxyStorage implements IProxy {
       // Otherwise misconfigured proxy could return 407:
       // https://github.com/rlidwka/sinopia/issues/254
       //
-      if (this.proxy === false) {
+      if (!this.proxy) {
         headers['X-Forwarded-For'] = (req.headers['x-forwarded-for'] ? req.headers['x-forwarded-for'] + ', ' : '') + req.connection.remoteAddress;
       }
     }