Add let keyword sample

Block scoping can be surprising, and sometimes confusing, in Javascript. With
es6, we have access to the let keyword to remove this pain

Source: https://egghead.io/lessons/the-let-keyword#/tab-code

es6/let_keyword.js

@@ -64,3 +64,33 @@ fs.forEach(function (f) {
 // 7
 // 8
 // 9
+
+function varFunc(){
+  var previous = 0;
+  var current = 1;
+  var i;
+  var temp;
+
+  for(i = 0; i < 10; i+=1){
+    temp = previous;
+    previous = current;
+    current = temp + current;
+  }
+  console.log(current);
+}
+
+function letFunc(){
+  let previous = 0;
+  let current = 1;
+
+  for(let i = 0; i < 10; i+=1){
+    let temp = previous;
+    previous = current;
+    current = temp + current;
+  }
+
+  console.log(current);
+}
+
+varFunc();
+letFunc();