Removed cache invalidation header when adding label through Amdin API

no issue

- Adding labels doesn't cause any content to invalidate, similarly to adding members. Unlike it's caunterpart - tags, there is no dependent "frontend" content that would become invalid

core/server/api/canary/labels.js

@@ -64,9 +64,7 @@ module.exports = {
 
     add: {
         statusCode: 201,
-        headers: {
-            cacheInvalidate: true
-        },
+        headers: {},
         options: [
             'include'
         ],

test/api-acceptance/admin/labels_spec.js

@@ -0,0 +1,51 @@
+const path = require('path');
+const should = require('should');
+const supertest = require('supertest');
+const sinon = require('sinon');
+const testUtils = require('../../utils');
+const localUtils = require('../../regression/api/canary/admin/utils');
+const config = require('../../../core/shared/config');
+
+const ghost = testUtils.startGhost;
+
+let request;
+
+describe('Labels API', function () {
+    after(function () {
+        sinon.restore();
+    });
+
+    before(function () {
+        return ghost()
+            .then(function () {
+                request = supertest.agent(config.get('url'));
+            })
+            .then(function () {
+                return localUtils.doAuth(request);
+            });
+    });
+
+    it('Can add', function () {
+        const label = {
+            name: 'test'
+        };
+
+        return request
+            .post(localUtils.API.getApiQuery(`labels/`))
+            .send({labels: [label]})
+            .set('Origin', config.get('url'))
+            .expect('Content-Type', /json/)
+            .expect('Cache-Control', testUtils.cacheRules.private)
+            .expect(201)
+            .then((res) => {
+                should.not.exist(res.headers['x-cache-invalidate']);
+                const jsonResponse = res.body;
+                should.exist(jsonResponse);
+                should.exist(jsonResponse.labels);
+
+                jsonResponse.labels.should.have.length(1);
+                jsonResponse.labels[0].name.should.equal(label.name);
+                jsonResponse.labels[0].slug.should.equal(label.name);
+            });
+    });
+});