Do not set up underscore.string globally.

cms/static/js/certificates/models/signatory.js

@@ -3,8 +3,7 @@
 define([ // jshint ignore:line
     'underscore',
     'backbone',
-    'backbone-relational',
-    'underscore.string'
+    'backbone-relational'
 ],
 function(_, Backbone) {
     'use strict';

lms/envs/common.py

@@ -1248,7 +1248,7 @@ base_vendor_js = [
     'js/vendor/jquery.cookie.js',
     'js/vendor/url.min.js',
     'common/js/vendor/underscore.js',
-    'js/vendor/underscore.string.min.js',
+    'common/js/vendor/underscore.string.js',
 
     # Make some edX UI Toolkit utilities available in the global "edx" namespace
     'edx-ui-toolkit/js/utils/global-loader.js',