fix metro-file-map spamming watchman warnings (#1260)

Summary:
Metro file map attempts to dedupe warnings but it doesn't correctly match against the message and instead throws all of them at once.

 {F1497196903}

This PR accounts for when there's only recrawled file to fix deduping

Changelog:

  Changelog: [Fix] watchman crawl warnings dedupe correctly now

Pull Request resolved: #1260

Test Plan: All modified and coverable lines are covered by tests ✅

Reviewed By: GijsWeterings

Differential Revision: D56595950

Pulled By: arushikesarwani94

fbshipit-source-id: 94230de83740f2c46c9cc991c622847ed99b9d1e

packages/metro-file-map/src/watchers/RecrawlWarning.js

@@ -19,7 +19,7 @@
 export default class RecrawlWarning {
   static RECRAWL_WARNINGS: Array<RecrawlWarning> = [];
   static REGEXP: RegExp =
-    /Recrawled this watch (\d+) times, most recently because:\n([^:]+)/;
+    /Recrawled this watch (\d+) times?, most recently because:\n([^:]+)/;
 
   root: string;
   count: number;