Fix error with checking config changes

scripts/content.js

@@ -177,7 +177,7 @@ async function runner() {
 
     for (let key in config) {
         if (config.hasOwnProperty(key)
-                && (!_.isEqual(config[key], prev_config[key]) || prev_config[key] === null)) {
+                && !_.isEqual(config[key], prev_config[key])) {
             console.log(`Config change: ${key}, ${prev_config[key]} => ${config[key]}`);
 
             // reduce countdown if frequency is reduced