refactor [cdnjs] integration (#1668)

* pass error object to InvaildResponse()

this prevents us from throwing
TypeError: Cannot read property 'stack' of undefined
when we attempt to parse invalid json

* refactor [cdnjs] integration

services/cdnjs/cdnjs.js

@@ -0,0 +1,61 @@
+'use strict';
+
+const BaseService = require('../base');
+const {
+  checkErrorResponse,
+  asJson,
+} = require('../../lib/error-helper');
+const { NotFound } = require('../errors');
+const { addv: versionText } = require('../../lib/text-formatters');
+const { version: versionColor} = require('../../lib/color-formatters');
+
+module.exports = class Cdnjs extends BaseService {
+  async handle({library}) {
+    const apiUrl = 'https://api.cdnjs.com/libraries/' + library + '?fields=version';
+    const json = await this._sendAndCacheRequest(apiUrl, {
+      headers: { 'Accept': 'application/json' }
+    }).then(checkErrorResponse.asPromise())
+      .then(asJson);
+
+    if (Object.keys(json).length === 0) {
+      /* Note the 'not found' response from cdnjs is:
+         status code = 200, body = {} */
+      throw new NotFound();
+    }
+    const version = json.version || 0;
+
+    return {
+      message: versionText(version),
+      color: versionColor(version)
+    };
+  }
+
+  // Metadata
+  static get defaultBadgeData() {
+    return { label: 'cdnjs' };
+  }
+
+  static get category() {
+    return 'version';
+  }
+
+  static get url() {
+    return {
+      base: 'cdnjs/v',
+      format: '(.*)',
+      capture: ['library']
+    };
+  }
+
+  static get examples() {
+    return [
+      {
+        previewUrl: 'jquery',
+        keywords: [
+          'cdn',
+          'cdnjs'
+        ]
+      }
+    ];
+  }
+};