style: Fixed most styles (according to standardjs)

Trees/DepthFirstSearch.js

@@ -25,13 +25,13 @@ function traverseDFS (root) {
 }
 
 function searchDFS (tree, value) {
-  var stack = []
+  const stack = []
 
   stack.push(tree[0])
 
   while (stack.length !== 0) {
     for (let i = 0; i < stack.length; i++) {
-      var node = stack.pop()
+      const node = stack.pop()
 
       if (node.value === value) {
         return node
@@ -47,7 +47,7 @@ function searchDFS (tree, value) {
   return null
 }
 
-var tree = [
+const tree = [
   { value: 6, left: 1, right: 2 },
   { value: 5, left: 3, right: 4 },
   { value: 7, left: null, right: 5 },