✨ Added support for v4 API in Content API SDK

refs TryGhost/Product#514

- Ghost 4.0 ships with a new set of APIs and v4 is a stable cut from the canary API

packages/content-api/lib/index.js

@@ -1,6 +1,6 @@
 import axios from 'axios';
 
-const supportedVersions = ['v2', 'v3', 'canary'];
+const supportedVersions = ['v2', 'v3', 'v4', 'canary'];
 const name = '@tryghost/content-api';
 
 export default function GhostContentAPI({url, host, ghostPath = 'ghost', version, key}) {

packages/content-api/test/content-api-test/v4.test.js

@@ -0,0 +1,37 @@
+// Switch these lines once there are useful utils
+// const testUtils = require('./utils');
+
+const should = require('should');
+
+const {getInstance} = require('../utils/ghost-server-mock');
+const GhostContentApi = require('../../cjs/content-api');
+
+describe('GhostContentApi v4', function () {
+    let server;
+    const config = {
+        version: 'v4',
+        key: '0123456789abcdef0123456789'
+    };
+
+    before(function (done) {
+        server = getInstance(config, (serverURL) => {
+            config.url = serverURL;
+            done();
+        });
+    });
+
+    after(function () {
+        server.close();
+    });
+
+    it('works', function (done) {
+        const api = new GhostContentApi(config);
+
+        server.once('url', ({pathname}) => {
+            should.equal(pathname, '/ghost/api/v4/content/posts/');
+            done();
+        });
+
+        api.posts.browse();
+    });
+});