Don't use deprecated Buffer() constructor

src/electron-injected.js

@@ -137,7 +137,7 @@ window.systemSetAsWallpaperCentered = c => {
 
 	const file_reader = new FileReader();
 	file_reader.onloadend = () => {
-		const buffer = new Buffer(file_reader.result);
+		const buffer = Buffer.from(file_reader.result);
 		fs.writeFile(imgPath, buffer, err => {
 			if(err){
 				return show_error_message("Failed to set as desktop background: couldn't write temporary image file.", err);