Revert "Update diff-dom package to 3.1.0"

This reverts commit 01b97986f6.

app/assets/javascripts/updateContent.js

@@ -2,7 +2,7 @@
   "use strict";
 
   var queues = {};
-  var dd = new diffDOM.DiffDOM();
+  var dd = new diffDOM();
 
   var getRenderer = $component => response => dd.apply(
     $component.get(0),

gulpfile.js

@@ -105,7 +105,7 @@ const javascripts = () => {
       paths.npm + 'hogan.js/dist/hogan-3.0.2.js',
       paths.npm + 'jquery/dist/jquery.min.js',
       paths.npm + 'query-command-supported/dist/queryCommandSupported.min.js',
-      paths.npm + 'diff-dom/browser/diffDOM.js',
+      paths.npm + 'diff-dom/diffDOM.js',
       paths.npm + 'timeago/jquery.timeago.js',
       paths.npm + 'textarea-caret/index.js'
     ]))

package.json

@@ -20,7 +20,7 @@
   "dependencies": {
     "@babel/core": "7.4.0",
     "@babel/preset-env": "7.4.2",
-    "diff-dom": "https://github.com/fiduswriter/diffDOM/archive/v3.1.0.tar.gz",
+    "diff-dom": "2.3.1",
     "govuk-elements-sass": "3.1.2",
     "govuk_frontend_toolkit": "8.1.0",
     "govuk_template_jinja": "0.24.1",
@@ -45,8 +45,5 @@
     "gulp-sass-lint": "1.4.0",
     "jshint": "2.10.2",
     "jshint-stylish": "2.2.1"
-  },
-  "peerDependencies": {
-    "rollup": "1.10.0"
   }
 }