replace underscore with our own

we only need like 5 simple functions

src/test/tasks-test.js

@@ -13,7 +13,7 @@ const BoxError = require('../boxerror.js'),
     paths = require('../paths.js'),
     safe = require('safetydance'),
     tasks = require('../tasks.js'),
-    _ = require('underscore');
+    _ = require('../underscore.js');
 
 describe('task', function () {
     const { setup, cleanup } = common;
@@ -23,7 +23,7 @@ describe('task', function () {
 
     let taskId;
 
-    let TASK = {
+    const TASK = {
         type: 'tasktype',
         args: [ 1 ],
         percent: 0,