fix eslint

src/background/shuffle.js

@@ -3,12 +3,12 @@
  * @param {Array} a items An array containing the items.
  */
 module.exports = function shuffle(a) {
-    let j, x, i;
-    for (i = a.length - 1; i > 0; i--) {
-        j = Math.floor(Math.random() * (i + 1));
-        x = a[i];
-        a[i] = a[j];
-        a[j] = x;
-    }
-    return a
+	let j, x, i;
+	for (i = a.length - 1; i > 0; i--) {
+		j = Math.floor(Math.random() * (i + 1));
+		x = a[i];
+		a[i] = a[j];
+		a[j] = x;
+	}
+	return a
 }