Fix bad routing regex for docs & blogs (#795)

* fix bad routing regex for docs & blogs

* extract to routing.js & add test

* add more test case

* address code review

* prettier

lib/core/routing.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+const escapeStringRegexp = require('escape-string-regexp');
+
+function docsRouting(baseUrl) {
+  return new RegExp(`^${escapeStringRegexp(baseUrl)}docs\/.*html$`);
+}
+
+function blogRouting(baseUrl) {
+  return new RegExp(`^${escapeStringRegexp(baseUrl)}blog\/.*html$`);
+}
+
+module.exports = {
+  docsRouting,
+  blogRouting,
+};