fix: add core-js/fn/array/flat-map import to no-undefined-types to ensure flatMap support

Babel expects such to be polyfilled through core-js

Author: brettz9

package.json

@@ -22,6 +22,7 @@
     "babel-plugin-add-module-exports": "^1.0.2",
     "babel-plugin-istanbul": "^5.1.4",
     "chai": "^4.2.0",
+    "core-js": "^3.1.4",
     "eslint": "^5.14.1",
     "eslint-config-canonical": "^17.1.1",
     "gitdown": "^2.5.8",

src/rules/noUndefinedTypes.js

@@ -1,3 +1,5 @@
+// eslint-disable-next-line import/no-unassigned-import
+import 'core-js/fn/array/flat-map';
 import _ from 'lodash';
 import {parse as parseType, traverse} from 'jsdoctypeparser';
 import iterateJsdoc, {parseComment} from '../iterateJsdoc';