chore: Use let instead of var to declare mutable variables

Author: prantlf

tasks/instructions/setViewport.js

@@ -6,9 +6,9 @@ module.exports = {
   },
 
   perform: function (grunt, target, client, command, options) {
-    var setViewport = command.setViewport
-    var lastViewport = options.lastViewport
-    var prefix
+    const lastViewport = options.lastViewport
+    let setViewport = command.setViewport
+    let prefix
     if (!(setViewport.width && setViewport.height)) {
       prefix = 'original '
       setViewport = options.viewport

tasks/instructions/wait.js

@@ -6,7 +6,7 @@ module.exports = {
   },
 
   perform: function (grunt, target, client, command, options) {
-    var wait = command.wait
+    let wait = command.wait
     if (!Array.isArray(wait)) {
       wait = wait ? [wait] : []
     }