fix: revert

Author: jamesgeorge007

lib/BannerPlugin.js

@@ -38,7 +38,7 @@ class BannerPlugin {
 
 		validateOptions(schema, options, "Banner Plugin");
 
-		if (["string", "function"].indexOf(typeof options) !== -1) {
+		if (typeof options === "string" || typeof options === "function") {
 			options = {
 				banner: options
 			};