deps: Upgrade and move underscore.js from static/third to npm

- Remove `underscore.js` from `static/third` and fetch it from `npm`.
- Upgrade `underscore.js` to 1.8.3.
- Bump up the `PROVISION_VERSION` to 4.2.

Part of zulip#1709

docs/THIRDPARTY

@@ -187,11 +187,6 @@ Files: static/third/spectrum/*
 Copyright: 2013 Brian Grinstead
 License: Expat
 
-Files: static/third/underscore/underscore.js
-Copyright: 2009-2015 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
-License: Expat
-Comment: https://github.com/jashkenas/underscore/blob/master/LICENSE
-
 Files: static/third/xdate/*
 Copyright: 2010 C. F., Wong
 License: Expat

docs/testing-with-node.md

@@ -91,7 +91,7 @@ For all the modules where you want to run actual code, add a statement
 like the following to the top of your test file:
 
 >     add_dependencies({
->         _: 'third/underscore/underscore.js',
+>         _: 'node_modules/underscore/underscore.js',
 >         util: 'js/util.js',
 >         Dict: 'js/dict.js',
 >         Handlebars: 'handlebars',
@@ -165,4 +165,3 @@ asserts, the *actual* value comes first, the *expected* value second.
 
 The test runner (`index.js`) automatically runs all .js files in the
 frontend\_tests/node directory.
-

frontend_tests/node_tests/message_list_view.js

@@ -1,4 +1,4 @@
-var _ = require('third/underscore/underscore.js');
+var _ = require('node_modules/underscore/underscore.js');
 var MessageListView = require('js/message_list_view.js');
 
 add_dependencies({

frontend_tests/zjsunit/finder.js

@@ -2,7 +2,7 @@ var finder = (function () {
 
 var exports = {};
 
-var _ = require('third/underscore/underscore.js');
+var _ = require('node_modules/underscore/underscore.js');
 var fs = require('fs');
 var path = require('path');
 

frontend_tests/zjsunit/index.js

@@ -2,7 +2,7 @@ global.assert = require('assert');
 require('node_modules/string.prototype.codepointat/codepointat.js');
 
 global.Dict = require('js/dict');
-global._ = require('third/underscore/underscore.js');
+global._ = require('node_modules/underscore/underscore.js');
 var _ = global._;
 
 // Find the files we need to run.

frontend_tests/zjsunit/namespace.js

@@ -1,6 +1,6 @@
 var namespace = (function () {
 
-var _ = require('third/underscore/underscore.js');
+var _ = require('node_modules/underscore/underscore.js');
 var exports = {};
 
 var dependencies = [];

frontend_tests/zjsunit/render.js

@@ -3,7 +3,7 @@ var render = (function () {
 var exports = {};
 
 var fs = require('fs');
-var _ = require('third/underscore/underscore.js');
+var _ = require('node_modules/underscore/underscore.js');
 var Handlebars = require('handlebars');
 
 function template_dir() {

package.json

@@ -15,6 +15,7 @@
     "jquery-validation": "1.15.1",
     "plotly.js": "1.19.2",
     "string.prototype.codepointat": "0.2.0",
+    "underscore": "1.8.3",
     "webpack": "1.12.2",
     "winchan": "0.2.0",
     "zxcvbn": "4.4.1"