Fixed Ember.copy deprecations

refs TryGhost/Ghost#10310
- https://emberjs.com/deprecations/v3.x/#toc_ember-runtime-deprecate-copy-copyable

app/components/gh-token-input/trigger.js

@@ -1,6 +1,5 @@
 import EmberPowerSelectMultipleTrigger from 'ember-power-select/components/power-select-multiple/trigger';
 import {assert} from '@ember/debug';
-import {copy} from '@ember/object/internals';
 import {get} from '@ember/object';
 import {isBlank} from '@ember/utils';
 
@@ -31,7 +30,8 @@ export default EmberPowerSelectMultipleTrigger.extend({
             // ember-drag-drop's sortable-objects has two-way bindings and will
             // update EPS' selected value directly. We have to create a copy
             // after sorting in order to force the onchange action to be triggered
-            this.get('select').actions.select(copy(this.get('select.selected')));
+            let selectedCopy = this.select.selected.slice();
+            this.get('select').actions.select(selectedCopy);
         },
 
         // copied directly from EPS, the default behaviour of stopping propagation

app/controllers/editor.js

@@ -6,7 +6,6 @@ import isNumber from 'ghost-admin/utils/isNumber';
 import {alias, mapBy} from '@ember/object/computed';
 import {computed} from '@ember/object';
 import {inject as controller} from '@ember/controller';
-import {copy} from '@ember/object/internals';
 import {htmlSafe} from '@ember/string';
 import {isBlank} from '@ember/utils';
 import {isArray as isEmberArray} from '@ember/array';
@@ -319,7 +318,7 @@ export default Controller.extend({
         // set mobiledoc equal to what's in the editor but create a copy so that
         // nested objects/arrays don't keep references which can mean that both
         // scratch and mobiledoc get updated simultaneously
-        this.set('post.mobiledoc', copy(this.get('post.scratch'), true));
+        this.set('post.mobiledoc', JSON.parse(JSON.stringify(this.post.scratch)));
         this.set('post.status', status);
 
         // Set a default title

lib/koenig-editor/addon/components/koenig-editor.js

@@ -22,7 +22,6 @@ import {A} from '@ember/array';
 import {MOBILEDOC_VERSION} from 'mobiledoc-kit/renderers/mobiledoc';
 import {assign} from '@ember/polyfills';
 import {camelize, capitalize} from '@ember/string';
-import {copy} from '@ember/object/internals';
 import {getContentFromPasteEvent} from 'mobiledoc-kit/utils/parse-utils';
 import {getLinkMarkupFromRange} from '../utils/markup-utils';
 import {getOwner} from '@ember/application';
@@ -313,7 +312,7 @@ export default Component.extend({
                 // `payload.files` is special because it's set by paste/drag-n-drop
                 // events and can't be copied for security reasons
                 let {files} = payload;
-                let payloadCopy = copy(payload, true);
+                let payloadCopy = JSON.parse(JSON.stringify(payload));
                 payloadCopy.files = files;
 
                 // all of the properties that will be passed through to the

lib/koenig-editor/addon/components/koenig-slash-menu.js

@@ -3,7 +3,6 @@ import layout from '../templates/components/koenig-slash-menu';
 import {CARD_MENU} from '../options/cards';
 import {assign} from '@ember/polyfills';
 import {computed, set} from '@ember/object';
-import {copy} from '@ember/object/internals';
 import {htmlSafe} from '@ember/string';
 import {isEmpty} from '@ember/utils';
 import {run} from '@ember/runloop';
@@ -164,7 +163,7 @@ export default Component.extend({
         }).compact();
 
         // we need a copy to avoid modifying the object references
-        let sections = copy(matchedItems, true);
+        let sections = JSON.parse(JSON.stringify(matchedItems));
 
         if (sections.length) {
             set(sections[0].items[0], 'selected', true);